Pascal's Triangle II 杨辉三角

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<vector<int>> tri;
        if(rowIndex==0)
        {
            vector<int> c;
            c.push_back(1);
            return c;
        }
        vector<int> b;
        b.push_back(0);
        b.push_back(1);
        b.push_back(0);
        tri.push_back(b);
        
        for(int i=1;i<=rowIndex;i++)
        {
            vector<int> a;
            a.push_back(0);
            for(int j=1;j<=i+1;j++)
                a.push_back(tri[i-1][j-1]+tri[i-1][j]);
            a.push_back(0);
            tri.push_back(a);
        }
        vector<int> res;
        for(int i=1;i<=rowIndex+1;i++)
        {
            res.push_back(tri[rowIndex][i]);
        }
        
        return res;
        
    }
};