104.Maximum Depth of Binary Tree

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

104. 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, 10⁴].
• -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

Ron ChenThu, 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;
}

MarsgoatThu, 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));
    }
}

JimThu, Feb 16, 2023

Reference

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