leetcode:118 Pascal's Triangle－每日編程第二十四題

Pascal's Triangle

Total Accepted: 66425 Total Submissions: 210900 Difficulty: Easy

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,

Return

[

     [1],

    [1,1],

   [1,2,1],

  [1,3,3,1],

 [1,4,6,4,1]

]

思路：

1).注意numRows爲0直接返回空的vector容器

2).每一行依據上一行生成

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> ans;
        if(numRows==0){
            return ans;
        }
        vector<int> vec;
        vec.push_back(1);
        ans.push_back(vec);
        for(int i=1;i<numRows;i++){
            vec.clear();
            vec.push_back(1);
            for(int j=0;j<i-1;j++){
                vec.push_back(ans[i-1][j]+ans[i-1][j+1]);
            }
            vec.push_back(1);
            ans.push_back(vec);
        }
        return ans;
    }
};