Pascal's Triangle

Easy

leetcode· Java· 2026-08-11Problem link ↗

ArrayDynamic Programming

Runtime

1 ms

Beats 95.33%

Memory

43.7 MB

Beats 16.5%

Problem

Given an integer numRows, return the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

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]]

Constraints:

1 <= numRows <= 30

Solution

Java

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

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> result = new ArrayList<>();
        for (int i = 0; i < numRows; i++) {
            List<Integer> row = new ArrayList<>();
            for (int j = 0; j <= i; j++) {
                if (j == 0 || j == i) {
                    row.add(1);
                } else {
                    row.add(result.get(i - 1).get(j - 1) + result.get(i - 1).get(j));
                }
            }
            result.add(row);
        }
        return result;
    }
}