Pascal's Triangle

帕斯卡三角形，主要考察vector的用法。

vector<vector<int> > generate(int numRows){vector<vector<int> > result;vector<int> tmp;result.clear();tmp.clear();int i,j;if(numRows == 0)return result;else if(numRows == 1){tmp.push_back(1);result.push_back(tmp);return result;}else if(numRows == 2){tmp.push_back(1);result.push_back(tmp);tmp.push_back(1);result.push_back(tmp);return result;}else{tmp.push_back(1);result.push_back(tmp);tmp.push_back(1);result.push_back(tmp);for(i = 2; i < numRows; i++){tmp.clear();            tmp.push_back(1);for(j = 1;j<=i-1;j++){tmp.push_back(result[i-1][j-1]+result[i-1][j]);}tmp.push_back(1);result.push_back(tmp);            }}return result;
}

上次怎么写这个麻烦，第二次写得简练许多

    vector<vector<int> > generate(int numRows){
        vector<vector<int> > res;
        vector<int> tmp, last;
        if(numRows == 0)
            return res;
        int i,j; 
        for(i = 0; i < numRows; i++){
            tmp = vector<int>(i+1, 0);
            tmp[0] = 1;
            tmp[i] = 1;
            for(j = 1; j < i; j++)
                tmp[j] = last[j-1] + last[j];
            res.push_back(tmp);
            last = tmp;
        }
        return res;
    }