Pascal's Triangle II

class Solution {
public:
    vector<int> getRow(int rowIndex) {
          vector<int> v;
          if( rowIndex < ) return v;

          v.push_back();
          if(rowIndex == ) return v;

          v.push_back();
          if(rowIndex == ) return v;

           vector<int> v1;

          for(int row=;row<=rowIndex;row++){

                v1.push_back();
             int pre_len = v.size();
             for(int i=;i<pre_len-;i++){
                v1.push_back(v[i]+v[i+]);
             }
                v1.push_back();
                v=v1;      //vector 拷贝好方便啊
                v1.clear();
          }
          return v;
    }
};