E118.杨辉三角

dp, https://leetcode.cn/problems/pascals-triangle/

思路：写两个循环即可

class Solution 
{
public:
    vector<vector<int>> generate(int numRows) 
    {
        vector<vector<int>> ans;
        for (int i = 0; i < numRows; i++)
        {
            ans.push_back(vector<int>());
            for (int j = 0; j < i + 1; j++)
            {
                if (j == 0 || j == i)
                    ans[i].push_back(1);
                else
                    ans[i].push_back(ans[i - 1][j - 1] + ans[i - 1][j]);
            }
        }
        return ans;

    }
};