Invert Binary Tree

Description

Invert a binary tree.

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

to

     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.

Tags: tree

思路

反转二叉树。通过前序遍历，依次调换每个节点的两个子节点即可。

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null || (root.left == null && root.right == null)) {
            return root;
        }
    
        TreeNode tmpNode = root.left;
        root.left = invertTree(root.right);
        root.right = invertTree(tmpNode);
    
        return root;
    }
}

kotlin(180ms/92.86%):

class Solution {
    fun invertTree(root: TreeNode?): TreeNode? {
        if (root == null) return null
        val tmp = root.left
        root.left = invertTree(root.right)
        root.right = invertTree(tmp)
        return root
    }
}

结语

如果你同我们一样热爱数据结构、算法、LeetCode，可以关注我们 GitHub 上的 LeetCode 题解：LeetCode-Solution