剑指28 对称二叉树

剑指28 对称二叉树

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root == null)
            return true;
        return check(root, root);
    }
    private boolean check(TreeNode left, TreeNode right) {
        if (left == null && right == null)
            return true;
        if (left == null || right == null)
            return false;
        return (left.val == right.val) && check(left.right, right.left) && check(right.left, left.right);
    }
}