/**
 * 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) {
        return isMirror(root,root);
    }

    public boolean isMirror(TreeNode t1,TreeNode t2){
        if(t1 == null && t2 == null) return true;
        if(t1 == null || t2 == null) return false;
        return (t1.val == t2.val) && isMirror(t1.right,t2.left) && isMirror(t1.left,t2.right);
    }
}