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;
    }