Pascal's Triangle

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]]      

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