Pascal's Triangle

题目：

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

[     [1],    [1,1],   [1,2,1],  [1,3,3,1], [1,4,6,4,1]]

代码如下：

vector<vector<int> > generate(int numRows) {
        vector<vector<int> > result;
        if(numRows<=0)return result;
        vector<int> tmp1(1,1);
        result.push_back(tmp1);
        if(numRows==1)return result;
        tmp1.push_back(1);
        result.push_back(tmp1);
        if(numRows==2)return result;
        for(int i=2;i<numRows;i++)
        {
            vector<int> tmp(1,1);
            for(int j=1;j<result[i-1].size();j++)
            {
                tmp.push_back(result[i-1][j-1]+result[i-1][j]);
            }
            tmp.push_back(1);
            result.push_back(tmp);
        }
        return result;
    }