LeetCode 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:

c++

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