226反转二叉树 Invert Binary Tree

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 fuck off.

翻转二叉树

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode InvertTree(TreeNode root) {
        if(root==null||(root.left==null&&root.right==null)) return root;
        var tem = root.left;
        root.left = root.right;
        root.right = tem;
        if(root.right!=null){
            InvertTree(root.right);
        }
        if(root.left!=null){
            InvertTree(root.left);
        }
        return root;
    }
}

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