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Symmetric Tree

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Description

https://leetcode.com/problems/symmetric-tree/description/

Solution

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if (root == NULL) return true;
        TreeNode* left = root->left;
        TreeNode* right = root->right;
        
        return check(left, right);
    }
    
    bool check(TreeNode* l, TreeNode* r) {
        if (l == NULL && r == NULL) return true;
        if (l == NULL || r == NULL) return false;
        if (l->val != r->val) return false;
        
        return this->check(l->left, r->right) && this->check(l->right, r->left);
    }
};