Leetcode notes 118. Yang Hui triangle

Title Description

Topic linking

Given a nonnegative integer numRows, Generate 「 Yang hui triangle 」 Before numRows That's ok .

stay 「 Yang hui triangle 」 in , Each number is the sum of the numbers at the top left and right of it .

Example 1:

Input : numRows = 5
Output : [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
Example 2:

Input : numRows = 1
Output : [[1]]

Tips :

1 <= numRows <= 30

Ideas

It's simulation , Pay attention to recurrence relationship $$\begin{gathered} ans[i][j]=ans[i-1][j-1]+ans[i-1][j]（j!=0||i） \\ ans[i][j]=1(j=0||i) \end{gathered}$$

among ans[i][j] Means Yang Hui triangle No i Xing di j individual

Code

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>(i + 1));
            for(int j = 0; j < i + 1; ++j)
            {
    
                if(j == 0 || j == i)
                {
    
                    ans[i][j] = 1;
                }
                else ans[i][j] = ans[i - 1][j - 1] + ans[i - 1][j];
            }
        }
        return ans;
    }
};