算法 Java Leetcode Golang

Invert a binary tree.

Question

Invert a binary tree.
See it on Leetcode

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For example, given:
     4
   /   \
  2     7
 / \   / \
1   3 6   9
It should return:
     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 fuck off.

Solution in Java, C++ and C

  • java
  • cpp
  • c
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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) return null;
        TreeNode node = new TreeNode(root.val);
        node.left = invertTree(root.right);
        node.right = invertTree(root.left);
        return node;
    }
}

Solution in Python, Javascript and CSharp

  • python
  • js
  • cs
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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def invertTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if root == None: return None  
        root.left, root.right = self.invertTree(root.right), self.invertTree(root.left)  
        return root

Solution in Golang

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/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func invertTree(root *TreeNode) *TreeNode {
    if root == nil {
        return nil
    }
    left := invertTree(root.Left)
    right := invertTree(root.Right)
    root.Left = right
    root.Right = left
    return root
}