Pascal's Triangle

class Solution {public:    vector<vector<int> > generate(int numRows) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector<vector<int>> ans;        vector<int> vec1,vec2;        if(numRows==0)return ans;        vec1.push_back(1);        ans.push_back(vec1);        int i,j;        for(i=1;i<numRows;++i){                        vec2.resize(i+1);            vec2[0]=vec1[0];            vec2[i]=vec1[i-1];            for(j=1;j<i;++j){                               vec2[j]=vec1[j-1]+vec1[j];               }            ans.push_back(vec2);            vec1=vec2;        }        return ans;    }};