572. 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 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.

/** * 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 isSubtree(TreeNode s, TreeNode t) { StringBuilder sb1 = new StringBuilder(); StringBuilder sb2 = new StringBuilder(); helper(sb1, s); helper(sb2, t); if (sb1.toString().contains(sb2)) return true; else return false; } private void helper(StringBuilder sb, TreeNode root) { if (root == null) { sb.append(",,"); return; } sb.append(',').append(root.val); helper(sb, root.left); helper(sb, root.right); } }