LeetCode 逆波兰表达式求值

LeetCode150.逆波兰表达式求值.

题目

代码

public class Solution 
{    
    public int EvalRPN(string[] tokens) 
    {        
        if (tokens.Length == 1)            
            return Convert.ToInt32(tokens[0]);        
        double x = 0 / 0.0;        
        int num = (int)x;        
        int jnum = num;        
        Stack<int> stack = new Stack<int>();        
        stack.Push(Convert.ToInt32(tokens[0]));        
        stack.Push(Convert.ToInt32(tokens[1]));        
        for (int i = 2; i < tokens.Length; i++)        
        {
            if (tokens[i] == "*" || tokens[i] == "/" || tokens[i] == "+" || tokens[i] == "-")            
            {                
                int p = stack.Peek();                
                stack.Pop();                
                int q = stack.Peek();                
                stack.Pop();                
                char k = Convert.ToChar(tokens[i]);                
                switch (k)                
                {                    
                    case '*':                        
                        num = q * p;                        
                        break;                    
                    case '/':                        
                        num = q / p;                        
                        break;                    
                    case '+':                        
                        num = q + p;                        
                        break;                    
                    case '-':                        
                        num = q - p;                        
                        break;                    
                    default:                        
                        return jnum;                
                }                
                stack.Push(num);            
            }            
            else                
                stack.Push(Convert.ToInt32(tokens[i]));            
        }            
        return num;    
    }
}

前面写的太繁琐了，化简了一下没想到速度飙升。

public class Solution 
{    
    public int EvalRPN(string[] tokens) 
    {        
        if (tokens.Length == 1)            
            return Convert.ToInt32(tokens[0]);        
        double x = 0 / 0.0;        
        int jnum = (int)x;        
        Stack<int> stack = new Stack<int>();        
        for (int i = 0; i < tokens.Length; i++)        
        {
            if (tokens[i] == "*" || tokens[i] == "/" || tokens[i] == "+" || tokens[i] == "-")            
            {                
                int p = stack.Pop();                
                int q = stack.Pop();                
                char k = Convert.ToChar(tokens[i]);                
                switch (k)                
                {                    
                    case '*':                        
                        stack.Push(q * p);                        
                        break;                    
                    case '/':                        
                        stack.Push(q / p);                        
                        break;                    
                    case '+':                       
                        stack.Push(q + p);                        
                        break;                    
                    case '-':                                                
                        stack.Push(q - p);                        
                        break;                    
                    default:                        
                        return jnum;                
                }            
            }            
            else                
                stack.Push(Convert.ToInt32(tokens[i]));            
        }            
        return stack.Pop();    
    }
}