101Symmetric Tree

/**
 * Definition for a binary tree node.
 * 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)) return false;
if(left.val==right.val){
return dfs(left.left,right.right)&&dfs(left.right,right.left);
}else{
return false;
}
}
}