Leetcode 101. symmetrical binary tree problem-solving ideas and implemented in C ++

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Method One: recursive

Problem-solving ideas:

First determine whether the current root root is null, and if so, returns true;

IsSame then calls the function, it is determined whether the left and right node satisfies the requirements of symmetry;

In isSame function, the core idea is recursive compare r1-> left == r2-> right and r1-> right == r2-> left.

/**
 * 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) return true;
        else return isSame(root->left, root->right);
    }
    bool isSame(TreeNode* r1, TreeNode* r2){
        if(!r1 || !r2) return r1 == r2;
        else{
            return (r1->val == r2->val) && isSame(r1->left, r2->right) && isSame(r1->right, r2->left);
        }
    }
};