C++ 代码

/**
 * 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;
        }
        return isSymmetric(root->left,root->right);
    }
    bool isSymmetric(TreeNode* left,TreeNode* right){
        if(!left||!right){
            return !left&&!right;
        }
        return (left->val==right->val)&&isSymmetric(left->left, right->right)&&isSymmetric(left->right, right->left);
    }
};