118. Pascal's Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal’s triangle.

In Pascal’s triangle, each number is the sum of the two numbers directly above it.

Example:

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

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Pascal’s Triangle.

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