[LeetCode]101 Symmetric Tree

/**
* 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 || (root.left == null && root.right == null))
return true;

return help(root.left, root.right);
}

// DFS
private boolean help(TreeNode l, TreeNode r)
{
if (l == null && r == null)
return true;
if (l == null && r != null)
return false;
if (l != null && r == null)
return false;

return (l.val == r.val) && help(l.left, r.right) && help(l.right, r.left);
}
}