判断一颗二叉树是不是另外一颗的子结构

 1 /**
 2 public class TreeNode {
 3     int val = 0;
 4     TreeNode left = null;
 5     TreeNode right = null;
 6 
 7     public TreeNode(int val) {
 8         this.val = val;
 9 
10     }
11 
12 }
13 */
14 public class Solution {
15     public boolean HasSubtree(TreeNode root1,TreeNode root2) {
16         
17         if(root2 == null)
18             return false;
19         
20         return DFS(root1, root2);
21     }
22     
23     private boolean DFS(TreeNode root1, TreeNode root2) {
24         
25           if(root1 == null)
26             return false;
27         
28         if(IsSubTree(root1, root2))
29             return true;
30         
31         return HasSubtree(root1.left, root2) | HasSubtree(root1.right, root2);  
32     }
33     
34     private boolean IsSubTree(TreeNode root1, TreeNode root2) {
35         
36         if(root2 == null)
37             return true;
38         else {
39             if(root1 == null || root1.val != root2.val)
40                 return false;
41             return IsSubTree(root1.left, root2.left) & IsSubTree(root1.right, root2.right);
42         }
43         
44     }
45 }