[LeetCode]Pascal's Triangle

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]

]

思考：边界单独考虑。

class Solution {

private:

    vector<vector<int> > res;

    vector<int> ans;

public:

    vector<vector<int> > generate(int numRows) {

        if(numRows==0) return res;

        int row=0;

        while(row<numRows)

        {

            ans.clear();

            for(int i=0;i<=row;i++)

            {

                if(i==0||i==row) ans.push_back(1);

                else ans.push_back(res[row-1][i-1]+res[row-1][i]);

            }

            row++;

            res.push_back(ans);

        }

        return res;

    }

};