PHP 实现翻转二叉树

PHP 实现翻转二叉树

author: he xiaodong date: 2020-07-06
翻转二叉树

翻转一棵二叉树。

示例:

输入:

     4
   /   \
  2     7
 / \   / \
1   3 6   9

输出:

     4
   /   \
  7     2
 / \   / \
9   6 3   1

来源:力扣(LeetCode) 链接:https://leetcode-cn.com/problems/invert-binary-tree

解题思路

递归法: 主要是遍历一下二叉树,将左边的值赋值给右边,遍历完也是交换完了。

迭代法: 将二叉树压入队列,然后循环队列,一个个节点弹出来,每个节点交换左右子树的值,迭代完毕也是交换完毕

php 递归法代码

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     public $val = null;
 *     public $left = null;
 *     public $right = null;
 *     function __construct($value) { $this->val = $value; }
 * }
 */
class Solution {

    /**
     * @param TreeNode $root
     * @return TreeNode
     */
    function invertTree($root) {
        if ($root == null) return null;
        // 保存右子树
        $rightTree = $root->right;
        // 交换左右子树的位置
        $root->right = $this->invertTree($root->left);
        $root->left = $this->invertTree($rightTree);
        return $root;
    }
}

php 迭代法代码

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     public $val = null;
 *     public $left = null;
 *     public $right = null;
 *     function __construct($value) { $this->val = $value; }
 * }
 */
class Solution {

    /**
     * @param TreeNode $root
     * @return TreeNode
     */
    function invertTree($root) {
        if ($root == null) return null;
        $queue = new SplQueue();
        $queue->enqueue($root);

        while (!$queue->isEmpty()) {
            $node = $queue->dequeue();
            list($node->left, $node->right) = [$node->right, $node->left];
            if ($node->left) {
                $queue->enqueue($node->left);
            }
            if ($node->right) {
                $queue->enqueue($node->right);
            }
        }
        
        return $root;
    }
}

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