pascals-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]
]

程序：

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        vector<vector<int>> res;
        if(numRows==0)
            return res;
        vector<int> v(1,1);
        res.push_back(v);
        if(numRows==1)
            return res;
        v.push_back(1);
        res.push_back(v);
        if(numRows==2)
            return res;
        int n=numRows-2;
        v.clear();
        while(n)
        {
            v.push_back(1);
            int len=res.size();
            for(int i=0;i<res[len-1].size()-1;i++)
                v.push_back(res[len-1][i]+res[len-1][i+1]);
            v.push_back(1);
            res.push_back(v);
            v.clear();
            n--;
        }
        return res;
    }
};