输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

1 package com.algorithm; 2  3 /*class TreeNode { 4  int val = 0; 5  TreeNode left = null; 6  TreeNode right = null; 7  public TreeNode(int val) { 8  this.val = val; 9  }10  }*/11 public class HasSubtreeTest {12     class TreeNode {13         int val = 0;14         TreeNode left = null;15         TreeNode right = null;16 17         public TreeNode(int val) {18             this.val = val;19         }20     }21 22     public boolean HasSubtree(TreeNode root1, TreeNode root2) {23         boolean result = false;// 返回结果24         if (root1 != null && root2 != null) {25             if (root1.val == root2.val)26                 result = IsTree1HasTree2(root1, root2);// 递归遍历27             if (!result) // 如果根结点不行，那么继续向左右子树遍历28                 result = IsTree1HasTree2(root1.left, root2);29             if (!result)30                 result = IsTree1HasTree2(root1.right, root2);31         }32         return result;33     }34 35     public boolean IsTree1HasTree2(TreeNode root1, TreeNode root2) {36         // 如果root1 为空 并且 root2不为空，那么代表并没有找到37         if (root1 == null && root2 != null)38             return false;39         // 如果根2 为空 ，则代表当前结点有40         if (root2 == null)41             return true;42         // 如果结点值不相等，那么返回false43         if (root1.val != root2.val)44             return false;45         // 再左右遍历子树46         return IsTree1HasTree2(root1.left, root2.left)47                 && IsTree1HasTree2(root1.right, root2.right);48     }49 50     public static void main(String[] args) {51 52     }53 }