【LeetCode】Pascal's Triangle (杨辉三角)

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]]

code :

class Solution {public:    vector<vector<int> > generate(int numRows) {        // Note: The Solution object is instantiated only once and is reused by each test case.        vector<vector<int> > res;        if(numRows == 0)            return res;        for(int i = 1; i <= numRows; i++)        {            vector<int> onelevel;            onelevel.clear();            onelevel.push_back(1);            for(int j = 1; j < i; j++)            {                onelevel.push_back(res[i-2][j-1] + (j < i-1 ? res[i-2][j] : 0));            }            res.push_back(onelevel);        }        return res;    }};