【英文】杨辉三角

Foreword

LeetCode answers, using Java language

Problem

• https://leetcode-cn.com/problems/pascals-triangle/

Source code

import java.util.ArrayList;
import java.util.List;

class Solution {
    public List<List<Integer>> generate(int numRows) {

        // Create a numRows*numRows 2D array
        int[][] arr = new int[numRows][numRows];
        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j < i+1; j++) {
                /*
                    If it is the first column or the last column, assign it as 1
                    Otherwise, assign it as the sum of "the number in the same column of the previous row" and "the number in the previous column of the previous row"
                 */
                if (j==0 || j==i) {
                    arr[i][j] = 1;
                } else {
                    arr[i][j] = arr[i-1][j] + arr[i-1][j-1];
                }
            }
        }

        // Put the 2D array into a nested list (discard the placeholder 0 in the 2D array)
        List l = new ArrayList();
        for (int i = 0; i < numRows; i++) {
            List list = new ArrayList();
            for (int j = 0; j < i+1; j++) {
                list.add(arr[i][j]);
            }
            l.add(list);
        }

        return l;
    }

}

Done