leetcode[118]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]

]

class Solution {

public:

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

        vector<vector<int>> res;

        vector<int> curr;

        if(numRows<1)return res;

        if(numRows==1)

        {

            curr.push_back(1);

            res.push_back(curr);

            return res;

        }

        if(numRows==2)

        {

            curr.push_back(1);

            res.push_back(curr);

            curr.push_back(1);

            res.push_back(curr);

            return res;

        }

        curr.push_back(1);

        res.push_back(curr);

        curr.push_back(1);

        res.push_back(curr);

        curr.clear();

        for(int i=2;i<numRows;i++)

        {

            curr.resize(i+1);

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

            {

                if(j==0||j==i)curr[j]=1;

                else

                {

                    curr[j]=res[i-1][j-1]+res[i-1][j];

                }

            }

            res.push_back(curr);

            curr.clear();

        }

        return res;

    }

};