104.Maximum Depth of Binary Tree
===

###### tags: `Easy`,`Tree`,`BFS`,`DFS`,`Binary Tree`

[104. Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/)

### 題目描述

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.

### 範例

**Example 1:**


Input: root = [3,9,20,null,null,15,7]
Output: 3

**Example 2:**

Input: root = [1,null,2]
Output: 2

**Constraints**:

* The number of nodes in the tree is in the range [0, 10^4^].
* -100 <= `Node.val` <= 100

### 解答
#### Python

class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1 if root else 0

> [name=Ron Chen][time=Thu, Feb 16, 2023]

#### Javascript

function maxDepth(root) {
  if (root === null) return 0;
  return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
}

非遞迴版本

function maxDepth2(root) {
  if (root === null) return 0;
  const queue = [root];
  let depth = 0;
  while (queue.length > 0) {
    const size = queue.length;
    for (let i = 0; i < size; i++) {
      const node = queue.shift();
      if (node.left !== null) queue.push(node.left);
      if (node.right !== null) queue.push(node.right);
    }
    depth++;
  }

  return depth;
}

> [name=Marsgoat][time=Thu, Feb 16, 2023]

#### C#

public class Solution {
    public int MaxDepth(TreeNode root) {
        return root == null ? 0 : 1 + Math.Max(MaxDepth(root.left), MaxDepth(root.right));
    }
}

> [name=Jim][time=Thu, Feb 16, 2023]

### Reference

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