[LeetCode] Symmetric Tree

https://leetcode.com/problems/symmetric-tree/

Symmetric Tree - LeetCode

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
        return check(root, root);
    }
    
    public boolean check(TreeNode leftNode, TreeNode rightNode) {
        
        if(leftNode == null && rightNode == null) {	// 둘다 자식node가 없으면 true
            return true;
        }
        
        if(leftNode == null || rightNode == null) {	// 한쪽만 자식node가 없으면 false
            return false;
        }
        
        if(leftNode.val != rightNode.val) {	// 값이 서로 다르면 false
            return false;
        }
        
        // 내려가면서 계속 확인
        return check(leftNode.left, rightNode.right) && check(leftNode.right, rightNode.left);       
    }
}