leetcode -- 119. Pascal's Triangle II

题目描述

题目难度：Easy
Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal’s triangle.

Note that the row index starts from 0.

Example:

Input: 3
Output: [1,3,3,1]
Follow up:

Could you optimize your algorithm to use only O(k) extra space?

AC代码

class Solution {
    public List<Integer> getRow(int rowIndex) {
        List<Integer> resList = new ArrayList<>();
        if(rowIndex < 0) return resList;
        resList.add(1);
        if(rowIndex == 0) return resList;
        resList.add(1);
        if(rowIndex == 1) return resList;
        int n1 = 1, n2 = 1;
        for(int i = 0;i < rowIndex - 1;i++){
            int size = resList.size();
            n1 = resList.get(0);
            n2 = resList.get(1);
            for(int j = 1;j <= size - 1;j++){
                resList.set(j, n1 + n2);
                n1 = n2;
                if(j + 1 <= size - 1) n2 = resList.get(j + 1);
            }
            resList.add(1);
        }
        return resList;
        // 1 4 3 1
        // 1 4 6 4 1
    }
}