No.226 翻转二叉树

给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。

示例 1：

输入：root = [4,2,7,1,3,6,9]
输出：[4,7,2,9,6,3,1]

示例 2：

输入：root = [2,1,3]
输出：[2,3,1]

示例 3：

输入：root = []
输出：[]

提示：

• 树中节点数目范围在 [0, 100] 内
• -100 <= Node.val <= 100

解题思路

实现

dfs - 深度优先搜索

/**
 * 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 {TreeNode}
 */
var invertTree = function (root) {
  if (!root) return null;
  let left = invertTree(root.left);
  let right = invertTree(root.right);
  root.left = right;
  root.right = left;
  return root;
};

bfs - 广度优先搜索

/**
 * 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 {TreeNode}
 */
var invertTree = function (root) {
  if (!root) return null;
  let queue = [];
  queue.push(root);
  while (queue.length) {
    let node = queue.shift();
    let temp = node.left;
    node.left = node.right;
    node.right = temp;
    if (node.left) queue.push(node.left);
    if (node.right) queue.push(node.right);
  }
  return root;
};