LeetCode-226. Invert Binary Tree

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问题描述

Given the root of a binary tree, invert the tree, and return its root.

Example:

img

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Input: root = [4,2,7,1,3,6,9]
Output: [4,7,2,9,6,3,1]

Constraints:

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

解答

方法一：递归
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/*
 * @Description: 226. Invert 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
 * @param {TreeNode} root
 * @return {TreeNode}
 */
const invertTree = function (root) {
  if (!root) {
    return root
  }

  let temp = root.left
  root.left = root.right
  root.right = temp

  invertTree(root.left)
  invertTree(root.right)

  return root
}
方法二：层序遍历
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/*
 * @Description: 226. Invert 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
 * @param {TreeNode} root
 * @return {TreeNode}
 */
const invertTree2 = function (root) {
  if (!root) {
    return root
  }

  let queue = [root]

  while (queue.length) {
    let curNode = queue.shift()
    let temp = curNode.left
    curNode.left = curNode.right
    curNode.right = temp
    if (curNode.left) {
      queue.push(curNode.left)
    }
    if (curNode.right) {
      queue.push(curNode.right)
    }
  }

  return root
}