Leetcode brush question: binary tree 06 (symmetric binary tree)

101. Symmetric binary tree

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Given a binary tree , Check if it is mirror symmetric .

package com.programmercarl.tree;

import java.util.*;

/** * @ClassName IsSymmetric * @Descriotion TODO * @Author nitaotao * @Date 2022/7/3 13:18 * @Version 1.0 * https://leetcode.cn/problems/symmetric-tree/ * 101.  Symmetric binary tree  **/
public class IsSymmetric {
    
    public boolean isSymmetric(TreeNode root) {
    
        // Only the root element , Directly through 
        if (root.left == null && root.right == null) {
    
            return true;
        }

        /** *  Flip the right half , Then the left and right sequences are traversed and compared  */
        if (root.left == null || root.right == null) {
    
            return false;
        }
        // Zuo Zishu doesn't understand , Right subtree transformation 
        reverse(root.right);
        return getNum(root.left, root.right);
    }

    public boolean getNum(TreeNode root1, TreeNode root2) {
    
        if ((root1 == null && root2 != null) || (root1 != null && root2 == null)) {
    
            return false;
        }

        if (root1 == null && root2 == null) {
    
            return true;
        }

        if (root1.val == root2.val) {
    
            boolean left = getNum(root1.left, root2.left);
            boolean right = getNum(root1.right, root2.right);
            // Come in again if you make a mistake 
            return left && right;
        } else {
    
            return false;
        }
    }

    public void reverse(TreeNode root) {
    
        if (root == null) {
    
            return;
        }
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        reverse(root.left);
        reverse(root.right);
    }

    public static void main(String[] args) {
    
        TreeNode node15 = new TreeNode(6, null, null);
        TreeNode node8 = new TreeNode(6, null, null);
        TreeNode node7 = new TreeNode(5, null, node15);
        TreeNode node4 = new TreeNode(5, node8, null);
        TreeNode node3 = new TreeNode(4, null, node7);
        TreeNode node2 = new TreeNode(4, node4, null);
        TreeNode node1 = new TreeNode(3, node2, node3);
        System.out.println(isSymmetric(node1));
    }
}

I vomited. , This question is disgusting .
The initial idea is to traverse the tree sequence , The results of each layer are compared with each other , It got stuck . Wrong afternoon .
Finally, change your thinking , First flip the right subtree , Then traverse and compare the left and right subtrees respectively .