LeetCode 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) {vector<vector<int> > iveclist;vector<int> ivec = { 1 }, last = { 1, 1 };if (numRows <= 0)return iveclist;else if (numRows == 1) {iveclist.push_back(ivec);return iveclist;}else if (numRows == 2) {iveclist.push_back(ivec);iveclist.push_back(last);return iveclist;}iveclist.push_back(ivec);iveclist.push_back(last);for (int i = 3; i <= numRows; i++) {ivec.clear();ivec.push_back(1);for (int j = 0; j < last.size() - 1; j++)ivec.push_back(last[j] + last[j + 1]);ivec.push_back(1);iveclist.push_back(ivec);last = ivec;}return iveclist;}};