LeetCode - 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) {
			 return true;
		 }
		 return dfs(root.left, root.right);
	 }
	 public boolean dfs(TreeNode left, TreeNode right) {
		 if(left==null && right==null) {
			 return true;
		 }
		 if((left!=null&&right==null) || (left==null&&right!=null) ||
				 left.val!=right.val) {
			 return false;
		 }
		 return dfs(left.left, right.right) && dfs(left.right, right.left);
	 }
}