[LeetCode] 226. Invert Binary Tree（反转二叉树）

• Difficulty: Easy

• Related Topics: Tree

Description

Invert a binary tree.

反转一棵二叉树

Examples

Example 1

Input:

     4
   /   
  2     7
 /    / 
1   3 6   9

Output:

     4
   /   
  7     2
 /    / 
9   6 3   1

Trivia

This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can't invert a binary tree on a whiteboard so f*** off.

Solution

“不能在白板上反转一棵二叉树的都是 **？”那今天的题目就不开 IDE 做了，直接裸写代码，相关的解释都在注释里了，自己看吧。

/**
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    fun invertTree(root: TreeNode?): TreeNode? {
        if (root == null) {
            return root
        }
        // 节点的左右子树交换
        val t = root.left
        root.left = root.right
        root.right = t
        
        // 对左右子树进行递归交换
        root.left = invertTree(root.left)
        root.right = invertTree(root.right)
        
        return root
    }
}