101. 对称二叉树

/**
 * 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;
        return isMirror(root->left,root->right);
    }

    bool isMirror(TreeNode* p,TreeNode* q){
        if(p==NULL && q==NULL) return true;
        if(p==NULL || q==NULL) return false;
        if(p->val==q->val && isMirror(p->left,q->right) && isMirror(p->right,q->left)){
            return true;
        }
        return false;
    }
};