[leetcode]Symmetric Tree

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool compare(TreeNode* l  , TreeNode* r){
        if(l == NULL && r == NULL) return true;
        if(l == NULL && r != NULL) return false;
        if(l != NULL && r == NULL) return false;
        if(l -> val != r -> val) return false;
        return compare(l -> right , r -> left) && compare(l -> left , r -> right);
    }
    bool isSymmetric(TreeNode *root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(root == NULL) return true;
        if(root -> left == NULL && root -> right == NULL) return true;
        
        return compare(root -> left , root -> right);
    }
};