Java语言程序设计(基础篇)(原书第10版) 第七章编程练习题

心血来潮补一下之前没做完的课后题，争取全部做完，欢迎大家评论指正。

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7-1 指定等级

import java.util.Scanner;

public class Program7_1 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter the number of students: ");
        int num = input.nextInt();

        int[] stu = new int[num];
        int best = 0;
        System.out.printf("Enter %d scores: ", num);
        for (int i = 0; i < num; i++) {
            stu[i] = input.nextInt();
            best = Math.max(best, stu[i]);
        }

        for (int i = 0; i < num; i++) {
            System.out.printf("Student %d score is %d and grade is ", i, stu[i]);
            if(stu[i] >= best - 10)
                System.out.println('A');
            else if(stu[i] >= best - 20)
                System.out.println('B');
            else if(stu[i] >= best - 30)
                System.out.println('C');
            else if(stu[i] >= best - 40)
                System.out.println('D');
            else
                System.out.println('F');
        }

        input.close();
    }

}

7-2 倒置输入的数

import java.util.Scanner;

public class Program7_2 {

   public static void main(String[] args) {
       System.out.print("Enter 10 integers: ");
       Scanner input = new Scanner(System.in);

       int[] num = new int[10];

       for (int i = 0; i < 10; i++)
           num[i] = input.nextInt();

       for (int i = 9; i >= 0; i--)
           System.out.print(num[i] + " ");
       System.out.println();
       input.close();
   }

}

7-3 计算数字的出现次数

import java.util.Scanner;

public class Program7_3 {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		
		int[] num = new int[101];
		int n;
		System.out.print("Enter the integers between 1 and 100: ");
		while(true) {
			n = input.nextInt();
			if(n == 0) break;
			num[n]++;
		}
		for(int i = 1; i < 101; i++) {
			if (num[i] != 0) {
				System.out.print(i + " occurs " + num[i] + " time");
				System.out.println(((num[i] > 1) ? 's' : ""));
			}
		}

		input.close();
	}

}

7-4 分析成绩

import java.util.Scanner;

public class Program7_4 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        double[] score = new double[101];

        System.out.println("Enter several scores, ending with a negative number: ");
        int cnt = 0;
        int sum = 0;
        int num = input.nextInt();
        while(num >= 0){
            score[num]++;
            sum += num;
            cnt++;
            num = input.nextInt();
        }
        double average = 1.0 * sum / cnt;
        int count1 = 0, count2 = 0;
        for (int i = 0; i <= 100; i++) {
            if(i >= average && score[i] != 0)
                count1 += score[i];
            else if(i < average && score[i] != 0)
                count2 += score[i];
        }
        System.out.printf("The average is %.2f\n", average);
        System.out.printf("%d score%s exceed the average score\n", count1, (count1 > 1) ? "s" : "");
        System.out.printf("%d score%s below the average score\n", count2, (count2 > 1) ? "s" : "");

        input.close();
    }

}

7-5 打印不同的数

import java.util.Scanner;

public class Program7_5 {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		
		int[] num = new int[10];
		int count = 0, m, flag;
		System.out.print("Enter ten number: ");
		for(int i = 0; i < 10; i++) {
			flag = 0;
			m = input.nextInt();
			for(int j = 0; j < i; j++)
				if(m == num[j]){
					flag = 1;
					break;
				}
			if(flag == 0) num[count++] = m;
		}	
		
		System.out.println("The number of distinct number is " + count);
		System.out.print("The distinct numbers are ");
		for(int i = 0; i < count; i++) {
			System.out.print(num[i]);
			if(i < count-1) System.out.print(" ");
		}
		System.out.println();

		input.close();
	}

}

7-6 修改程序清单5-15

public class Program7_6 {

    public static void main(String[] args) {
        final int NUMBER_OF_PRIMES = 50; // Number of primes to display
        final int NUMBER_OF_PRIMES_PER_LINE = 10; // Display 10 per line
        int count = 0; // Count the number of prime numbers
        int number = 2; // A number to be tested for primeness

        System.out.println("The first 50 prime numbers are \n");

        int[] prime = new int[50];

        // Repeatedly find prime numbers
        while (count < NUMBER_OF_PRIMES) {
            // Assume the number is prime
            boolean isPrime = true; // Is the current number prime?

            // Test if number is prime
            for (int i = 0; prime[i] <= Math.sqrt(number) && i < count; i++) {
                if(number % prime[i] == 0){
                    isPrime = false; // Set isPrime to false
                    break; // Exit the for loop
                }
            }

            // Print the prime number and increase the count
            if (isPrime) {
                prime[count] = number;
                count++;
            }

            // Check if the next number is prime
            number++;
        }

        for (int i = 0; i < count; i++) {
            System.out.print(prime[i] + " ");
            if((i+1) % NUMBER_OF_PRIMES_PER_LINE == 0)
                System.out.println();
        }
    }

}

7-7 统计一位数的个数

public class Program7_7 {
	public static void main(String[] args) {
		int[] count = new int[10];
		
		for(int i = 1; i <= 100; i++) {
			int m = (int)(Math.random() * 10);
			System.out.print(m + " ");
			if(i % 10 == 0) System.out.println();
			count[m]++;
		}
		for(int i = 0; i < 10; i++)
			System.out.println(i + " occurs " + count[i] + " times");
	}
	
}

7-8 求数组的平均值

import java.util.Scanner;

public class Program7_8 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter 10 double numbers: ");

        double[] num = new double[10];
        for (int i = 0; i < 10; i++)
            num[i] = input.nextDouble();

        System.out.printf("The average of the array is: %.2f\n", average(num));

        input.close();
    }

    public static int average(int[] array){
        int sum = 0;
        for (int i = 0; i < array.length; i++)
            sum += array[i];

        return sum / array.length;
    }

    public static double average(double[] array){
        double sum = 0.0;
        for (int i = 0; i < array.length; i++)
            sum += array[i];

        return 1.0 * sum / array.length;
    }

}

7-9 找出最小元素

import java.util.Scanner;

public class Program7_9 {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		double[] num = new double[10];
		
		System.out.print("Enter ten numbers: ");
		for(int i = 0; i < 10; i++)
			num[i] = input.nextDouble();
		
		System.out.println("The minimum number is: " + min(num));

		input.close();
	}

	public static double min(double[] array) {
		double min = array[0];
		for(int i = 1; i < array.length; i++)
			if(array[i] < min)
				min = array[i];
		
		return min;
	}

}

7-10 找出最小元素的下标

import java.util.Scanner;

public class Program7_10 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		double[] num = new double[10];
		
		System.out.print("Enter ten numbers: ");
		for(int i = 0; i < 10; i++)
			num[i] = input.nextDouble();
		
		System.out.println("The index of smallest element is: " + indexOfSmallestElement(num));

		input.close();
	}

	public static int indexOfSmallestElement(double[] array) {
		double min = array[0];
		int indexMin = 0;
		for(int i = 1; i < array.length; i++)
			if(array[i] < min) {
				min = array[i];
				indexMin = i;
			}
		
		return indexMin;
	}

}

7-11 统计学方面：计算标准差

import java.util.Scanner;

public class Program7_11 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter ten numbers: ");
        double[] num = new double[10];

        for (int i = 0; i < 10; i++)
            num[i] = input.nextDouble();

        System.out.printf("The mean is %.2f\n", mean(num));
        System.out.printf("The standard deviation is %.5f\n", deviation(num));

        input.close();
    }

    //Compute the deviation of an array of double values
    public static double deviation(double[] x){
        double sum = 0.0;
        double average = mean(x);
        for (int i = 0; i < 10; i++)
            sum += (x[i] - average) * (x[i] - average);

        return Math.sqrt(sum / 9);
    }

    //Compute the mean of an array of double values
    public static double mean(double[] x){
        double sum = 0.0;
        for (int i = 0; i < 10; i++)
            sum += x[i];

        return sum / 10;
    }

}

7-12 倒置数组

import java.util.Scanner;

public class Program7_12 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter ten numbers: ");

        int[] num = new int[10];
        for (int i = 0; i < 10; i++)
            num[i] = input.nextInt();

        num = reverse(num);
        for (int i = 0; i < 10; i++)
            System.out.print(num[i] + " ");
        System.out.println();

        input.close();
    }

    public static int[] reverse(int[] list){
        for (int i = 0; i < list.length / 2; i++) {
            int temp = list[i];
            list[i] = list[list.length - i - 1];
            list[list.length - i - 1] = temp;
        }
        return list;
    }

}

7-13 随机数选择器

public class Program7_13 {

	public static void main(String[] args) {
		
		System.out.println(getRandom(3,5,15,54));
	}

	public static int getRandom(int... numbers) {
		int m, flag = 0;
		while(true) {
			m = (int)(Math.random() * 55);
			for(int i = 0; i < numbers.length; i++)
				if(m == numbers[i]) {
					flag = 1;
					break;
				}
			if(flag == 0) break;
		}
		
		return m;
	}

}

7-14 计算gcd

import java.util.Scanner;

public class Program7_14 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter five numbers: ");
        int[] num = new int[5];
        for (int i = 0; i < 5; i++)
            num[i] = input.nextInt();

        System.out.println("The gcd of these five numbers is " + gcd(num));

        input.close();
    }

    public static int gcd(int... numbers){
        int gcd = numbers[0];
        for (int i = 1; i < numbers.length; i++) {
            int num = Math.min(gcd, numbers[i]);
            for (int j = num; j >= 1; j--)
                if(gcd % j == 0 && numbers[i] % j == 0){
                    gcd = j;
                    break;
                }
        }
        return gcd;
    }

}

7-15 消除重复

import java.util.Scanner;

public class Program7_15 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter ten numbers: ");
        int[] list = new int[10];

        for (int i = 0; i < 10; i++)
            list[i] = input.nextInt();

        System.out.print("The distinct numbers are: ");
        int[] ans = eliminateDuplicates(list);
        for (int i = 0; i < ans.length; i++)
            System.out.print(ans[i] + " ");
        System.out.println();
        input.close();
    }

    public static int[] eliminateDuplicates(int[] list){
        int[] num = new int[list.length];
        int count = 0;
        for (int value : list) {
            boolean flag = true;
            for (int j = 0; j < count; j++)
                if (value == num[j]) {
                    flag = false;
                    break;
                }
            if (flag) {
                num[count] = value;
                count++;
            }
        }
        int[] ans = new int[count];
        for (int i = 0; i < count; i++)
            ans[i] = num[i];
        return ans;
    }

}

7-16 执行时间

import java.util.Arrays;

public class Program7_16 {

    public static void main(String[] args) {
        final int NUMBER = 100000;
        int[] numbers = new int[NUMBER];

        for (int i = 0; i < NUMBER; i++)
            numbers[i] = (int) (Math.random() * (NUMBER + 1));

        int key = (int) (Math.random() * (NUMBER + 1));

        long startTime = System.currentTimeMillis();
        System.out.println(linearSearch(numbers, key));
        long endTime = System.currentTimeMillis();
        long executionTime = endTime - startTime;
        System.out.println("Execution time for linearSearch: " + executionTime);

        Arrays.sort(numbers);
        startTime = System.currentTimeMillis();
        System.out.println(binarySearch(numbers, key));
        endTime = System.currentTimeMillis();
        executionTime = endTime - startTime;
        System.out.println("Execution time for binarySearch: " + executionTime);
    }

    /** The method for finding a key in the list */
    public static int linearSearch(int[] list, int key) {
        for (int i = 0; i < list.length; i++) {
            if (key == list[i])
                return i;
        }
        return -1;
    }

    /** Use binary search to find the key in the list */
    public static int binarySearch(int[] list, int key) {
        int low = 0;
        int high = list.length - 1;

        while (high >= low) {
            int mid = (low + high) / 2;
            if (key < list[mid])
                high = mid - 1;
            else if (key == list[mid])
                return mid;
            else
                low = mid + 1;
        }

        return -low - 1; // Now high < low
    }

}

7-17 对学生排序

import java.util.Scanner;

public class Program7_17 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		
		System.out.print("Enter the number of students: ");
		int n = input.nextInt();
		
		String[] name = new String[n];
		double[] score = new double[n];
		
		System.out.println("Please enter the name and score of the students:");
		for(int i = 0; i < n; i++) {
			name[i] = input.next();
			score[i] = input.nextDouble();
		}
		scoreSort(name, score);
		
		System.out.println("name\t score\t");
		System.out.println("----------------");
		for(int i = 0; i < n; i++)
			System.out.printf("%-9s%-5.1f\n",name[i],score[i]);

		input.close();
	}

	public static void scoreSort(String[] name, double[] score) {
		String tempName;
		double tempScore;
		int k;
		for(int i = 0; i < score.length-1; i++) {
			k = i;
			for(int j = i+1; j < score.length; j++)
				if(score[j] > score[k])
					k = j;
			tempName = name[k]; name[k] = name[i]; name[i] = tempName;
			tempScore = score[k]; score[k] = score[i]; score[i] = tempScore;
		}
	}

}

7-18 冒泡排序

import java.util.Scanner;

public class Program7_18 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        double[] num = new double[10];

        System.out.print("Please enter ten numbers: ");
        for (int i = 0; i < num.length; i++)
            num[i] = input.nextDouble();

        bubbleSort(num);

        for (int i = 0; i < num.length; i++) {
            System.out.print(num[i]);
            if (i < num.length - 1) System.out.print("   ");
        }
        System.out.println();

        input.close();
    }

    public static void bubbleSort(double[] array) {
        double temp;

        for (int i = 0; i < array.length - 1; i++)
            for (int j = 0; j < array.length - 1 - i; j++)
                if (array[j] > array[j + 1]) {
                    temp = array[j];
                    array[j] = array[j + 1];
                    array[j + 1] = temp;
                }
    }
}

7-19 是否排好序了？

import java.util.Scanner;

public class Program7_19 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter list: ");
        int n = input.nextInt();
        int[] list = new int[n];
        for (int i = 0; i < n; i++)
            list[i] = input.nextInt();

        if(isSorted(list))
            System.out.println("The list is already sorted");
        else
            System.out.println("The list is not sorted");
    }

    public static boolean isSorted(int[] list){
        for (int i = 1; i < list.length; i++) {
            if(list[i] < list[i-1])
                return false;
        }
        return true;
    }

}

7-20 修改选择排序法

import java.util.Scanner;

public class Program7_20 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter ten numbers: ");
        double[] list = new double[10];
        for(int i = 0; i < 10; i++)
            list[i] = input.nextDouble();

        selectionSort(list);

        for (int i = 0; i < 10; i++)
            System.out.print(list[i] + "  ");
        System.out.println();
        input.close();
    }

    /** The method for sorting the numbers */
    public static void selectionSort(double[] list) {
        for (int i = list.length - 1; i > 0; i--) {

            double currentMax = list[i];
            int currentMaxIndex = i;

            for (int j = i-1; j >= 0; j--) {
                if (currentMax < list[j]) {
                    currentMax = list[j];
                    currentMaxIndex = j;
                }
            }

            if (currentMaxIndex != i) {
                list[currentMaxIndex] = list[i];
                list[i] = currentMax;
            }
        }
    }

}

7-21 游戏：豆机

import java.util.Scanner;

public class Program7_21 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter the number of balls to drop: ");
        int balls = input.nextInt();
        System.out.print("Enter the number of slots in the bean machine: ");
        int slot = input.nextInt();
        int[] slots = new int[slot];
        int maxBalls = 0;
        System.out.println();
        for(int i = 0; i < balls; i++){
            int count = 0;
            for (int j = 0; j < slot-1; j++) {
                int num = (int) (Math.random() * 2);
                if(num == 0)
                    System.out.print('L');
                else {
                    System.out.print('R');
                    count++;
                }
            }
            System.out.println();
            slots[count]++;
            maxBalls = Math.max(maxBalls, slots[count]);
        }
        System.out.println();

        for (int i = maxBalls; i >= 1; i--) {
            for (int j = 0; j < slot; j++) {
                if(slots[j] >= i)
                    System.out.print("0");
                else
                    System.out.print(" ");
            }
            System.out.println();
        }
    }

}

7-22 游戏：八皇后

public class Program7_22 {

    public static void main(String[] args) {
        int[] queen = new int[8];

        for (int i = 0; i < 8; i++)
            queen[i] = -1;
        queen[0] = 0;

        int row = 1;
        while (row >= 0 && row < 8) {
            boolean flag = false;
            for (int i = queen[row] + 1; i < 8; i++)
                if (check(row, i, queen)) {
                    flag = true;
                    queen[row] = i;
                    break;
                }
            if (queen[row] != -1 && flag)
                row++;
            else{
                queen[row] = -1;
                row--;
            }
        }

        for(int i = 0; i < 8; i++){
            for(int j = 0; j < queen[i]; j++)
                System.out.print("| ");
            System.out.print("|Q|");
            for(int j = queen[i]+1; j < 8; j++)
                System.out.print(" |");
            System.out.println();
        }
    }

    public static boolean check(int row, int col, int[] queen) {
        for (int i = 0; i < row; i++)
            if (queen[i] == col)
                return false;
        for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--)
            if (queen[i] == j)
                return false;
        for (int i = row - 1, j = col + 1; i >= 0 && j < 8; i--, j++)
            if (queen[i] == j)
                return false;
        return true;
    }

}

7-23 游戏：储物柜难题

public class Program7_23 {

    public static void main(String[] args) {
        boolean[] lockers = new boolean[101];

        for (int i = 1; i <= 100; i++)
            lockers[i] = false;

        for(int i = 1; i <= 100; i++){
            for(int j = i; j <= 100; j += i)
                lockers[j] = !lockers[j];
        }

        System.out.println("Opened lockers: ");
        for(int i = 1; i <= 100; i++)
            if(lockers[i])
                System.out.print(i + "  ");
    }

}

7-24 仿真：优惠券收集人问题

public class Program7_24 {

    public static void main(String[] args) {
        String[] suit = {"Spade", "Heart", "Diamond", "Club"};
        boolean[] check = new boolean[4];

        for (int i = 0; i < 4; i++)
            check[i] = false;

        int count = 0;

        while (!(check[0] && check[1] && check[2] && check[3]))
            count += checkPoker(check, suit);

        System.out.println("Numbers of picks: " + count);
    }

    public static int checkPoker(boolean[] check, String[] suit){
        String[] card = {"Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"};
        int[] poker = new int[52];
        for (int i = 0; i < 52; i++)
            poker[i] = i;

        for(int i = poker.length-1; i > 0; i--){
            int j = (int) (Math.random() * (i+1));
            int temp = poker[i];
            poker[i] = poker[j];
            poker[j] = temp;
        }

        int cnt = 0;

        while (true){
            cnt++;
            int n = (int) (Math.random() * 52);
            int color = n % 4, num = n % 13;
            if(!check[color]){
                check[color] = true;
                System.out.printf("%s of %s\n", card[num], suit[color]);
                break;
            }
        }
        return cnt;
    }

}

7-25 代数问题：解二次方程式

import java.util.Scanner;

public class Program7_25 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        double[] eqn = new double[3];
        double[] roots = new double[2];

        System.out.print("Enter a, b, c: ");
        for (int i = 0; i < 3; i++)
            eqn[i] = input.nextDouble();

        int num = solveQuadratic(eqn, roots);
        System.out.println("Number of roots: " + num);

        for (int i = 0; i < num; i++)
            System.out.print(roots[i] + "    ");
        System.out.println();
        input.close();
    }

    public static int solveQuadratic(double[] eqn, double[] roots){
        double a = eqn[0], b = eqn[1], c = eqn[2];

        double m = b*b - 4*a*c;
        double n = -b / (2*a);
        int num = 0;
        if(m < 0)
            num = 0;
        else if(m == 0) {
            roots[0] = n;
            num = 1;
        }
        else {
            roots[0] = n + Math.pow(m, 0.5) / (2 * a);
            roots[1] = n - Math.pow(m, 0.5) / (2 * a);
            num = 2;
        }
        return num;
    }

}

7-26 完全相同的数组

import java.util.Scanner;

public class Program7_26 {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		
		System.out.print("Enter list1: ");
		int n1 = input.nextInt();
		double[] list1 = new double[n1];
		for(int i = 0; i < n1; i++)
			list1[i] = input.nextDouble();
		
		System.out.print("Enter list2: ");
		int n2 = input.nextInt();
		double[] list2 = new double[n2];
		for(int i = 0; i < n2; i++)
			list2[i] = input.nextDouble();
		
		if(equals(list1, list2))
			System.out.println("Two lists are strictly identical");
		else
			System.out.println("Two lists are not strictly identical");

		input.close();
	}

	public static boolean equals(double[] list1, double[] list2) {
		if(list1.length != list2.length)
			return false;
		for(int i = 0; i < list1.length; i++)
			if(list1[i] != list2[i])
				return false;
		
		return true;
	}
}

7-27 相同的数组

import java.util.Scanner;

public class Program7_27 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		
		System.out.print("Enter list1: ");
		int n1 = input.nextInt();
		int[] list1 = new int[n1];
		for(int i = 0; i < n1; i++)
			list1[i] = input.nextInt();
		
		System.out.print("Enter list2: ");
		int n2 = input.nextInt();
		int[] list2 = new int[n2];
		for(int i = 0; i < n2; i++)
			list2[i] = input.nextInt();
		
		if(equals(list1, list2))
			System.out.println("Two lists are identical");
		else
			System.out.println("Two lists are not identical");
		
	}

	public static boolean equals(int[] list1, int[] list2) {
		java.util.Arrays.parallelSort(list1);
		java.util.Arrays.parallelSort(list2);
		if(list1.length != list2.length)
			return false;
		for(int i = 0; i < list1.length; i++)
			if(list1[i] != list2[i])
				return false;
		
		return true;
	}
}

7-28 数学方面：组合

import java.util.Scanner;

public class Program7_28 {

   public static void main(String[] args) {
       Scanner input = new Scanner(System.in);

       int[] numbers = new int[10];
       System.out.print("Enter 10 numbers: ");

       for (int i = 0; i < 10; i++)
           numbers[i] = input.nextInt();

       for (int i = 0; i < 10; i++)
           for (int j = i+1; j < 10; j++)
               System.out.printf("(%d, %d)\n", numbers[i], numbers[j]);

       input.close();
   }

}

7-29 游戏：选出四张牌

public class Program7_29 {

	public static void main(String[] args) {
		int[] poker = new int[52];
		String[] card = {"Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"};
		
		for(int i = 0; i < 52; i++)
			poker[i] = i;
		
		int count = 0;
		while(true){
			int sum = 0;
			for(int i = 1; i <= 4; i++){
				System.out.print(i + "\t");
				int j = (int) (Math.random() * 52);
				sum += j%13;
				System.out.println(card[j%13]);
			}
			if(sum == 24) break;
			count++;
			System.out.println();
		}
		System.out.println("count: " + count);
	}

}

7-30 模式识别方面：四个连续相等的数

import java.util.Scanner;

public class Program7_30 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter the number of values: ");
        int num = input.nextInt();

        int[] values = new int[num];
        System.out.print("Enter the values: ");
        for (int i = 0; i < num; i++)
            values[i] = input.nextInt();

        if(isConsecutiveFour(values))
            System.out.println("The list has consecutive fours");
        else
            System.out.println("The list has no consecutive fours");

        input.close();
    }

    public static boolean isConsecutiveFour(int[] values){
        for (int i = 0; i < values.length - 4; i++){
            boolean flag = true;
            for(int j = 1; j < 4; j++)
                if(values[i+j] != values[i]) {
                    flag = false;
                    break;
                }
            if(flag)
                return true;
        }
        return false;
    }

}

7-31 合并两个有序列表

import java.util.Scanner;

public class Program7_31 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter list1: ");
        int n1 = input.nextInt();
        int[] list1 = new int[n1];
        for (int i = 0; i < n1; i++)
            list1[i] = input.nextInt();

        System.out.print("Enter list2: ");
        int n2 = input.nextInt();
        int[] list2 = new int[n2];
        for (int i = 0; i < n2; i++)
            list2[i] = input.nextInt();

        System.out.print("The merged list is ");
        int[] ans = merge(list1, list2);
        for (int i = 0; i < ans.length; i++)
            System.out.print(ans[i] + " ");
        System.out.println();

        input.close();
    }

    public static int[] merge(int[] list1, int[] list2){
        int i = 0, j = 0, n = 0;
        int[] ans = new int[list1.length + list2.length];
        while(i != list1.length || j != list2.length){
            if(i == list1.length) {
                ans[n] = list2[j];
                j++;
                n++;
                continue;
            }
            if(j == list2.length) {
                ans[n] = list1[i];
                i++;
                n++;
                continue;
            }
            if(list1[i] <= list2[j]){
                ans[n] = list1[i];
                i++;
            }else{
                ans[n] = list2[j];
                j++;
            }
            n++;
        }
        return ans;
    }

}

7-32 划分列表

import java.util.Scanner;

public class Program7_32 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter list: ");
        int num = input.nextInt();
        int[] list = new int[num];

        for(int i = 0; i < num; i++)
            list[i] = input.nextInt();

        partition(list);

        System.out.print("After the partition. the list is ");
        for (int i = 0; i < num; i++)
            System.out.print(list[i] + " ");
        System.out.println();

        input.close();
    }

    public static int partition(int[] list){
        int index = 0, large = 0;
        for(int i = 1; i < list.length; i++){
            if(list[i] < list[index]){
                int temp = list[i];
                list[i] = list[index];
                list[index] = temp;
                index = i;
            }else{
                if(large + index >= list.length)
                    break;
                int temp = list[i];
                list[i] = list[list.length - large - 1];
                list[list.length - large - 1] = temp;
                large++;
                i--;
            }
        }
        return index;
    }

}

7-33 文化：中国生肖

import java.util.Scanner;

public class Program7_33 {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter a year: ");
        int year = input.nextInt();

        String[] zodiac = {"monkey", "rooster", "dog", "pig", "rat", "ox",
                "tiger", "rabbit", "dragon", "snake", "horse", "sheep"};

        System.out.println(zodiac[year % 12]);
    }

}

7-34 对字符串中的字符排序

import java.util.Scanner;

public class Program7_34 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		
		System.out.print("Enter a string: ");
		String s = input.next();
		
		System.out.println(sort(s));
		
	}

	public static char[] sort(String s){
		int len = s.length();
		char[] str = s.toCharArray();
		for(int i = 0; i < len; i++){
			int k = i;
			for(int j = i+1; j < len; j++)
				if(str[j] < str[k]) k = j;
			char temp = str[i];
			str[i] = str[k];
			str[k] = temp;
		}
		
		return str;
	}
}

7-35 游戏：猜字游戏

import java.util.Scanner;

public class Program7_35 {

    public static void main(String[] args) {
        String[] words = {"write", "that", "program", "java", "software", "system", "project", "chess"};
        Scanner input = new Scanner(System.in);
        char c;
        do{
            int missCount = 0;
            int t = (int) (Math.random() * (words.length));
            String str = words[t];
            String m = "";
            for (int i = 0; i < str.length(); i++)
                m += '*';
            while(str.compareTo(m) != 0){
                System.out.print("(Guess) Enter a letter in word " + m + " > ");
                char letter = input.next().charAt(0);
                if(str.indexOf(letter) != -1){
                    if(m.indexOf(letter) != -1)
                        System.out.println("    " + letter + " is already in the word");
                    else{
                        String alter = "";
                        for (int i = 0; i < str.length(); i++) {
                            if (str.charAt(i) == letter)
                                alter += letter;
                            else
                                alter += m.charAt(i);
                        }
                        m = alter;
                    }
                }else {
                    System.out.println("    " + letter + " is not in the word");
                    missCount++;
                }
            }
            System.out.println("The word is " + str + ". " +
                    "You missed " + missCount + " time" + ((missCount > 1) ? 's' : ""));
            System.out.print("Do you want to guess another word? Enter y or n > ");
            c = input.next().charAt(0);
        }while(c == 'y');
    }

}