Subtree

 1 /**
 2  * Definition of TreeNode:
 3  * public class TreeNode {
 4  *     public int val;
 5  *     public TreeNode left, right;
 6  *     public TreeNode(int val) {
 7  *         this.val = val;
 8  *         this.left = this.right = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     /**
14      * @param T1, T2: The roots of binary tree.
15      * @return: True if T2 is a subtree of T1, or false.
16      */
17     public boolean isSubtree(TreeNode T1, TreeNode T2) {
18         if (T2 == null)
19             return true;
20         if (T1 == null)
21             return false;
22 
23         boolean[] result = new boolean[1];
24         helper(T1, T2, result);
25         return result[0];
26 
27     }
28 
29     public void helper(TreeNode T1, TreeNode T2, boolean[] result) {
30         if (T1 == null)
31             return;
32 
33         if (T1.val == T2.val) {
34             if (contains(T1, T2)) {
35                 result[0] = true;
36                 return;
37             }
38         }
39         helper(T1.left, T2, result);
40         helper(T1.right, T2, result);
41     }
42 
43     public boolean contains(TreeNode T1, TreeNode T2) {
44         if (T2 == null && T1 == null)
45             return true;
46         if (T1 == null || T2 == null)
47             return false;
48 
49         if (T1.val == T2.val) {
50             return contains(T1.left, T2.left) && contains(T1.right, T2.right);
51         }
52         return false;
53     }
54 }