Pascal's Triangle

/*
杨辉三角的简单应用 res[i][j] = res[i-1][j]+res[i-1][j-1](j>0&&j<i)
                   res[i][j] = 1 (j == 0|| j==i)
*/
class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        vector<vector<int> >res;
        for(int i = 0 ; i < numRows ; i++){
            res.push_back(vector<int>());
            for(int j = 0 ; j <= i ; j++){
                if(j == 0 || j == i) {
                    res[i].push_back(1);
                }else {
                     res[i].push_back(res[i-1][j]+res[i-1][j-1]);
                }
            }
        }
        return res;
    }
};