Pascal's Triangle leetcode

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]
]

 

 

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0 0
0[1]0
0[1 1]0
0[1 2 1]0
0[1 3 3 1]0
0[1 4 6 4 1]

帕斯卡三角形，它的值 a[i][j] = a[i-1][j-1] + a[i-1][j]; 注意如果i-1<0，则a[i-1]=0，也就是假设三角形周边的元素都是0

程序中我们可以直接让边缘的数值为1

vector<vector<int>> generate(int numRows) {
    vector<vector<int>> ret;
    for (int i = 0; i < numRows; ++i)
    {
        vector<int> row;
        for (int j = 0; j <= i; ++j)
        {
            if (j == 0 || j == i)
                row.push_back(1);
            else
                row.push_back(ret[i - 1][j - 1] + ret[i - 1][j]);
        }
        ret.push_back(row);
    }
    return ret;
}