# Maximum Depth of Binary Tree

Given the `root` of a binary tree, return *its maximum depth*.

A binary tree's **maximum depth** is the number of nodes along the longest path from the root node down to the farthest leaf node.

![](https://3269900549-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MIbwNq54Ge4eqsziHM7%2F-MPZD4ODtZqqEtuQ1Xdn%2F-MPZgS2wPWP83u6AFSYU%2Fmaxdepth%20prob%20desc.png?alt=media\&token=d8567a1a-2de7-4e62-a513-affe79c77b59)

**자료구조** : N/A

**알고리즘**\
1\. 재귀호출을 통해 잎노드까지 내려간다. - Null을 만날 때까지 재귀호출로 쭉 내려간다!\
2\. Null을 만나면 비로소 값을 가지게 된다! 0 또는 1. - left:0, right:0, Math.max(0,0)+1 = 1

**알고리즘을 Java로**

```java
package graph;
import java.util.*;

class TreeNode {
	     int val;
	     TreeNode left;
	     TreeNode right;
	     TreeNode() {}
	     TreeNode(int val) { this.val = val; }
	     TreeNode(int val, TreeNode left, TreeNode right) {
	         this.val = val;
	         this.left = left;
	         this.right = right;
	     }
	 }
public class MaxDepthBT {//recursive call

	public static void main(String[] args) {
		TreeNode root = new TreeNode(3);
		root.left = new TreeNode(1);
		root.right = new TreeNode(4);
		root.left.left = new TreeNode(5);
		root.left.right = new TreeNode(8);
		root.left.left.left = new TreeNode(7);
		
		System.out.println(solve(root));
	}
	
	public static int solve(TreeNode root) {
		if(root == null) return 0;
		
		int left = solve(root.left);
		int right = solve(root.right);
		return Math.max(left, right)+1;
	}

}

```


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