LeetCode-226-Flip Binary Tree (Simple)

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1. Description

Flip a binary tree.

2. Example

enter:

Output:

3. Analysis

Observe the input and output, take node "4" as the observation target, you can see that the root node "4" remains unchanged, its left child "2" and right child "7" have swapped positions, and the left child "2" is located The left subtree and the right subtree where the right child "7" is located have also exchanged positions as a whole. The same rule also exists in other nodes.
So we came to the conclusion,

The operation of flipping the binary tree includes:
(1) The root node remains unchanged;
(2) The left subtree and the right subtree are swapped.
(3) Flip the left subtree;
(4) Flip the right subtree.

4. Code

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    
    
    public TreeNode invertTree(TreeNode root)
    {
    
    
    	// 递归的终止条件
        if(root == null)
            return root;
        // 根非空的话，交换左右子树
        TreeNode cache = root.left;
        root.left = root.right;
        root.right = cache;
        // 翻转左子树
        invertTree(root.left);
        // 翻转右子树
        invertTree(root.right);
        return root;
    }
}

5. Verification

6. Source

1. LeetCode 226. Invert Binary Tree
   Source: LeetCode
   Link: https://leetcode-cn.com/problems/invert-binary-tree
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