LeetCode-104. Maximum Depth of Binary Tree

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问题描述

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.

Constraints:

  • The number of nodes in the tree is in the range [0, 104].
  • -100 <= Node.val <= 100

解答

方法一：递归
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/*
 * @Description: 104. Maximum Depth of Binary Tree
 * @Author: libk
 * @Github: https://github.com/libk
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @description: 递归解法
 * @param {TreeNode} root
 * @return {number}
 */
const maxDepth = function (root) {
  if (!root) {
    return 0
  }

  return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1
}
方法二：层序遍历
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/*
 * @Description: 104. Maximum Depth of Binary Tree
 * @Author: libk
 * @Github: https://github.com/libk
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @description: 层序遍历的思想
 * @param {TreeNode} root
 * @return {number}
 */
const maxDepth = function (root) {
  if (!root) {
    return 0
  }

  let queue = [root]
  let res = 0
  while (queue.length) {
    let curLength = queue.length
    while (curLength) {
      let cur = queue.shift()
      if (cur.left) {
        queue.push(cur.left)
      }
      if (cur.right) {
        queue.push(cur.right)
      }
      curLength--
    }
    res++
  }
  return res
}