Symmetric Tree

Problem

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

        1
       / \
      2   2
     / \ / \
    3  4 4  3

But the following is not:

        1
       / \
      2   2
       \   \
       3    3

Code - Java

/**
 * Definition for binary tree
 * public class TreeNode {
 *   int val;
 *   TreeNode left;
 *   TreeNode right;
 *   TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;
        return same(root.left, root.right);
    }

    private boolean same(TreeNode left, TreeNode right) {
        if (left == null && right == null) return true;
        if ((left == null && right != null) || (left != null && right == null)) return false;
        return left.val == right.val && same(left.left, right.right) && same(left.right, right.left);
    }
}

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