LeetCode_119. Pascal's Triangle II

Posted 2022-12-24 denggelin

 

119. Pascal‘s Triangle II

Easy

Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal‘s triangle.

Note that the row index starts from 0.

In Pascal‘s triangle, each number is the sum of the two numbers directly above it.

Example:

Input: 3
Output: [1,3,3,1]

Follow up:

Could you optimize your algorithm to use only O(k) extra space?

 

package leetcode.easy;

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

public class PascalSTriangleII 
	@org.junit.Test
	public void test() 
		System.out.println(getRow(3));
	

	public List<Integer> getRow(int rowIndex) 
		List<Integer> row = new ArrayList<>();
		row.add(1);
		if (rowIndex == 0) 
			return row;
		
		for (int rowNum = 1; rowNum <= rowIndex; rowNum++) 
			List<Integer> prevRow = row;
			row = new ArrayList<>();
			row.add(1);
			for (int j = 1; j < rowNum; j++) 
				row.add(prevRow.get(j - 1) + prevRow.get(j));
			
			row.add(1);
		
		return row;