118. Yanghui triangle

Given a nonnegative integer numRows, Generate 「 Yang hui triangle 」 Before numRows That's ok .

stay 「 Yang hui triangle 」 in , Each number is the sum of the numbers at the top left and right of it .

Example 1:

 Input : numRows = 5
 Output : [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Example 2:

 Input : numRows = 1
 Output : [[1]]

Tips :

1 <= numRows <= 30

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