Leetcode 101. Symmetric Tree

/**
 * 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* left, TreeNode* right) {
        if(left == NULL && right == NULL) {
            return true;
        }
        if(left == NULL || right == NULL) {
            return false;
        }
        return left->val == right->val && isMirror(left->left, right->right) && isMirror(left->right, right->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 == NULL) {
            return true;
        }
        queue<TreeNode*> nodes;
        nodes.push(root);
        nodes.push(root);
        while(!nodes.empty()) {
            TreeNode* left = nodes.front();
            nodes.pop();
            TreeNode* right = nodes.front();
            nodes.pop();
            if(left == NULL && right == NULL) {
                continue;
            }
            if(left == NULL || right == NULL) {
                return false;
            }
            if(left->val == right->val) {
                nodes.push(left->left);
                nodes.push(right->right);
                nodes.push(left->right);
                nodes.push(right->left);
            }
            else {
                return false;
            }
        }
        return true;
    }
};