class Solution {
public boolean isSymmetric(TreeNode root) {
return recursion(root, root);
}
private boolean recursion(TreeNode first, TreeNode second){
if(first==null || second == null){
return first==second;
}
if(first.val!=second.val) return false;
if(recursion(first.left, second.right)){
return recursion(first.right, second.left);
}else{
return false;
}
}
}