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]
]

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