leetcode-118-pascal’s triangle

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]
]

给定一个数字N，生成前N行帕斯卡三角。

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