leetcode 101.对称二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool cmp(TreeNode* left,TreeNode* right){
        if(left==NULL&&right==NULL){
            return true;
        }else if(left!=NULL&&right==NULL){
            return false;
        }else if(left==NULL&&right!=NULL){
            return false;
        }else if(left!=NULL&&right!=NULL&&left->val!=right->val){
            return false;
        }
        bool isCmp;
        bool isOut=cmp(left->left,right->right);
        bool isIn=cmp(left->right,right->left);
        isCmp=isOut&&isIn;
        return isCmp;
    }
    bool isSymmetric(TreeNode* root) {
        if(root==NULL) return true;
        return cmp(root->left,root->right);
    }
};

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