leetcode 118. Pascal's Triangle

题目描述：

//题解

class Solution {
public:
    vector<vector<int> > ret;
    vector<vector<int>> generate(int numRows) {
        if(numRows <= 0)
            return ret;
        for(int i = 1 ; i <= numRows; i++ ){
            if(i == 1){
                vector<int> tmp;
                tmp.push_back(1);
                ret.push_back(tmp);
            }
            else if( i == 2){
                vector<int> tmp;
                tmp.push_back(1);
                tmp.push_back(1);
                ret.push_back(tmp);                
            }
            else{
                vector<int>  last = ret.back();
                vector<int> tmp;
                tmp.push_back(1);
                for(int j = 1; j < i-1; j++ ){
                    int num = last.at(j-1)+last.at(j);
                    tmp.push_back(num);
                }
                tmp.push_back(1);
                ret.push_back(tmp);    
            }
                
        }
        return ret;
    }
};