LeetCode - Easy - 637. Average of Levels in Binary Tree

古城微笑少年丶 2022-10-16 09:39 138阅读 0赞

## Topic ##

*  Tree

## Description ##

[https://leetcode.com/problems/average-of-levels-in-binary-tree/][https_leetcode.com_problems_average-of-levels-in-binary-tree]

Given the `root` of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within  1 0 − 5 10^\{-5\} 10−5 of the actual answer will be accepted.

**Example 1:**

![ddf0607022acc04c349f552f23662210.png][]

Input: root = [3,9,20,null,15,7]
    Output: [3.00000,14.50000,11.00000]
    Explanation: The average value of nodes on level 0 is 3, on level 1 is 14.5, and on level 2 is 11.
    Hence return [3, 14.5, 11].

**Example 2:**

![4612e9bd3973edc6a569e6a58f9f4dd4.png][]

Input: root = [3,9,20,15,7]
    Output: [3.00000,14.50000,11.00000]

**Constraints:**

*  The number of nodes in the tree is in the range  \[ 1 , 1 0 4 \] \[1, 10^4\] \[1,104\].
 *   − 2 31 ⩽ N o d e . v a l ⩽ 2 31 − 1 -2^\{31\} \\leqslant Node.val \\leqslant 2^\{31\} - 1 −231⩽Node.val⩽231−1

## Analysis ##

方法一：BFS

方法二：DFS

## Submission ##

import java.util.ArrayList;
    import java.util.LinkedList;
    import java.util.List;
    import java.util.stream.Collectors;
    
    import com.lun.util.BinaryTree.TreeNode;
    
    public class AverageOfLevelsInBinaryTree { 
    
    	// 方法一：BFS
    	public List<Double> averageOfLevels(TreeNode root) { 
    		LinkedList<TreeNode> queue = new LinkedList<>();
    
    		queue.offer(root);
    		List<Double> result = new ArrayList<>();
    
    		while (!queue.isEmpty()) { 
    
    			int size = queue.size(), originSize = size;
    			long sum = 0;
    
    			for (int i = 0; i < size; i++) { 
    				TreeNode node = queue.poll();
    
    				sum += node.val;
    
    				if (node.left != null)
    					queue.offer(node.left);
    
    				if (node.right != null)
    					queue.offer(node.right);
    
    			}
    			result.add(sum * 1.0 / originSize);
    		}
    
    		return result;
    	}
    
    	// 方法二：DFS
    	public List<Double> averageOfLevels2(TreeNode root) { 
    		List<long[]> levelSumAndCounts = new ArrayList<>();
    		averageOfLevels2(root, 0, levelSumAndCounts);
    		return levelSumAndCounts.stream().map(a -> a[0] * 1.0 / a[1]).collect(Collectors.toList());
    	}
    
    	private void averageOfLevels2(TreeNode node, int level, List<long[]> levelSumAndCounts) { 
    		if (node == null)
    			return;
    
    		if (levelSumAndCounts.size() == level) { 
    			levelSumAndCounts.add(new long[] { node.val, 1});
    		} else { 
    			long[] temp = levelSumAndCounts.get(level);
    			temp[0] += node.val;
    			temp[1]++;
    		}
    
    		averageOfLevels2(node.left, level + 1, levelSumAndCounts);
    		averageOfLevels2(node.right, level + 1, levelSumAndCounts);
    	}
    }

## Test ##

import static org.junit.Assert.*;
    
    import java.util.List;
    
    import org.junit.Test;
    
    import com.lun.util.BinaryTree;
    import com.lun.util.BinaryTree.TreeNode;
    
    public class AverageOfLevelsInBinaryTreeTest { 
    
    	private TreeNode bigRoot = BinaryTree.integers2BinaryTree(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, //
    			0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2147483647,2147483647,2147483647,2147483643,2147483645,2147483646,2147483646, //
    			2147483624,2147483646,2147483647,2147483646,2147483647,2147483647,2147483631,2147483647,2147483647,2147483647, //
    			2147483647,2147483631,2147483647,2147483647,2147483647,2147483647,2147483646,2147483646,2147483614,2147483646, //
    			2147483647,2147483646,2147483647,2147483646,2147483647,2147483646,2147483647,2147483646,2147483647,2147483646, //
    			2147483647,2147483646,2147483647,2147483646,2147483647,2147483646,2147483647,2147483646,2147483647,2147483646, //
    			2147483647,2147483644,2147483644,2147483647,2147483647,2147483644,2147483647,2147483647,2147483644,2147483647, //
    			2147483647,2147483644,2147483647,2147483647,2147483644,2147483647,2147483647,2147483644,2147483647,2147483647, //
    			2147483644,2147483647,2147483647,2147483644,2147483647,2147483647,2147483644,2147483647,2147483647,2147483644, //
    			2147483647,2147483647,2147483644,2147483647,2147483647,2147483644,2147483647,2147483647,2147483644,2147483647, //
    			2147483647,2147483644,2147483647,2147483647,2147483644,2147483647,2147483647,2147483642,2147483647,2147483647, //
    			2147483647,2147483636,2147483647,2147483647,2147483647,2147483647,2147483647,2147483647,2147483636,2147483647, //
    			2147483647,2147483647,2147483647,2147483647,2147483647,2147483636,2147483647,2147483647,2147483647,2147483647, //
    			2147483647,2147483647,2147483636,2147483647,2147483647,2147483647,2147483647,2147483647,2147483647,2147483636, //
    			2147483647,2147483647,2147483647,2147483647,2147483647,2147483647,2147483636,2147483647,2147483647,2147483647, //
    			2147483647,2147483647,2147483647,2147483636,2147483647,2147483647,2147483647,2147483647,2147483647,2147483647, //
    			2147483636,2147483647,2147483647,2147483647,2147483647,2147483647,2147483647,2147483636,2147483647,2147483647, //
    			2147483647,2147483647,2147483647,2147483647,2147483636,2147483647,2147483647,2147483647,2147483647,2147483647, //
    			2147483647,2147483636,2147483647,2147483647,2147483647,2147483647,2147483647,2147483647,2147483636,2147483647, //
    			2147483647,2147483647,2147483647,2147483647,2147483647,2147483636,2147483647,2147483647,2147483647,2147483647, //
    			2147483647,2147483647,2147483642,2147483642,2147483647,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483647,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483647,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642,2147483642, //
    			2147483642,-2147483647,-2147483647,-2147483647,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483638,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483643,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483643, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483643,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483643,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483643,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642,-2147483642, //
    			-2147483643,-2147483642,-2147483642,-2147483642,-2147483642,-2147483598,-2147483647,-2147483647,-2147483647, //
    			-2147483647,-2147483645,-2147483647,-2147483647,-2147483647,-2147483645,-2147483647,-2147483647,-2147483647, //
    			-2147483645,-2147483647,-2147483647,-2147483647,-2147483645,-2147483647,-2147483647,-2147483647,-2147483645, //
    			-2147483647,-2147483647,-2147483647,-2147483645,-2147483647,-2147483647,-2147483647,-2147483645,-2147483647, //
    			-2147483647,-2147483647,-2147483645,-2147483647,-2147483647,-2147483647,-2147483645,-2147483647,-2147483647, //
    			-2147483647,-2147483645,-2147483647,-2147483647,-2147483647,-2147483645,-2147483647,-2147483647,-2147483647, //
    			-2147483647,-2147483647,-2147483647,-2147483647,-2147483647,-2147483647,-2147483647,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647, //
    			-2147483644,-2147483647,-2147483647,-2147483644,-2147483600,-2147483646,-2147483646,-2147483646,-2147483646, //
    			-2147483646,-2147483646,-2147483646,-2147483646,-2147483646,-2147483646,-2147483646,-2147483647,-2147483647, //
    			-2147483525,-2147483647,-2147483647,-2147483644,-2147483647,-2147483647,-2147483647,-2147483646,-2147483647, //
    			-2147483336);
    
    	@Test
    	public void test() { 
    		AverageOfLevelsInBinaryTree obj = new AverageOfLevelsInBinaryTree();
    
    		double delta = 10e-5;
    		double[] expected = { 3.00000, 14.50000, 11.00000};
    		
    		List<Double> result1 = obj.averageOfLevels(BinaryTree.integers2BinaryTree(3, 9, 20, null, 15, 7));
    		List<Double> result2 = obj.averageOfLevels(BinaryTree.integers2BinaryTree(3, 9, 20, 15, 7));
    
    		for(int i = 0; i < expected.length; i++) { 
    			assertEquals(expected[i], result1.get(i), delta);
    			assertEquals(expected[i], result2.get(i), delta);
    		}
    		
    
    		List<Double> result3 = obj.averageOfLevels(BinaryTree.integers2BinaryTree(2147483647, 2147483647, 2147483647));
    		double[] expected3 = { 2147483647.00000, 2147483647.00000};
    		
    		for(int i = 0; i < expected3.length; i++) { 
    			assertEquals(expected3[i], result3.get(i), delta);
    		}
    		
    		List<Double> result4 = obj.averageOfLevels(bigRoot);
    		double[] expected4 = { 0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000};
    		
    		for(int i = 0; i < expected4.length; i++) { 
    			assertEquals(expected4[i], result4.get(i), delta);
    		}
    	}
    	
    	@Test
    	public void test2() { 
    		AverageOfLevelsInBinaryTree obj = new AverageOfLevelsInBinaryTree();
    		
    		double delta = 10e-5;
    		double[] expected = { 3.00000, 14.50000, 11.00000};
    		
    		List<Double> result1 = obj.averageOfLevels2(BinaryTree.integers2BinaryTree(3, 9, 20, null, 15, 7));
    		List<Double> result2 = obj.averageOfLevels2(BinaryTree.integers2BinaryTree(3, 9, 20, 15, 7));
    		
    		for(int i = 0; i < expected.length; i++) { 
    			assertEquals(expected[i], result1.get(i), delta);
    			assertEquals(expected[i], result2.get(i), delta);
    		}
    		
    		
    		List<Double> result3 = obj.averageOfLevels2(BinaryTree.integers2BinaryTree(2147483647, 2147483647, 2147483647));
    		double[] expected3 = { 2147483647.00000, 2147483647.00000};
    		
    		for(int i = 0; i < expected3.length; i++) { 
    			assertEquals(expected3[i], result3.get(i), delta);
    		}
    		
    		List<Double> result4 = obj.averageOfLevels2(bigRoot);
    		double[] expected4 = { 0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000,0.00000};
    		
    		for(int i = 0; i < expected4.length; i++) { 
    			assertEquals(expected4[i], result4.get(i), delta);
    		}
    	}
    }

[https_leetcode.com_problems_average-of-levels-in-binary-tree]: https://leetcode.com/problems/average-of-levels-in-binary-tree/
[ddf0607022acc04c349f552f23662210.png]: /images/20221014/39068b78a1764b978efb9f4c14ad034d.png
[4612e9bd3973edc6a569e6a58f9f4dd4.png]: /images/20221014/c5790c6690784bb99b2be69699ef2173.png