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