Subtree of Another Tree

This question is similar to check if two trees are symmetric or not.

https://leetcode.com/problems/subtree-of-another-tree/

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree that consists of a node in s and all of this node’s descendants. The tree s could also be considered as a subtree of itself.

Example 1:
Given tree s:

3
    / \
   4   5
  / \
 1   2

Given tree t:

4 
  / \
 1   2

Return true, because t has the same structure and node values with a subtree of s.

Example 2:
Given tree s:

3
    / \
   4   5
  / \
 1   2
    /
   0

Given tree t:

4
  / \
 1   2

Return false.

Here is the Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    String s1= "";
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if(t==null)
            return true;
        if(s == null)
            return false;
        if(isSymmetric(s,t))
            return true;
        return isSubtree(s.left,t) || isSubtree(s.right,t);
    }
    
    public static boolean isSymmetric(TreeNode left,TreeNode right){
        if(left ==  null || right == null)
            return left == right;
        if(left.val!=right.val)
            return false;
        return isSymmetric(left.left,right.left) && isSymmetric(left.right,right.right);
    }
}

Thank you for Reading!

Happy Coding!