LeetCode-543. Diameter of Binary Tree

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问题描述

Given the root of a binary tree, return the length of the diameter of the tree.

The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

The length of a path between two nodes is represented by the number of edges between them.

Example :

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Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].

Constraints:

  • The number of nodes in the tree is in the range [1, 104].
  • -100 <= Node.val <= 100

解答

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/*
 * @Description: 543. Diameter 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)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
const diameterOfBinaryTree = function (root) {
  let max = 0

  const dfs = (cur) => {
    if (!cur) {
      return 0
    }
    const left = dfs(cur.left)
    const right = dfs(cur.right)
    max = Math.max(max, left + right)
    return Math.max(left, right) + 1
  }
  dfs(root)
  return max
}