剑指Offer----树的子结构

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）

/**public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class Solution {    public boolean HasSubtree(TreeNode root1,TreeNode root2) {           boolean result = false;            if(root1 != null && root2 != null){                if(root1.val == root2.val){                    result = DoesTree1HaveTree2(root1,root2);                }                if(!result){result = HasSubtree(root1.left, root2);}                if(!result){result = HasSubtree(root1.right, root2);}            }            return result;    }      public boolean DoesTree1HaveTree2(TreeNode root1,TreeNode root2){            if(root1 == null && root2 != null) return false;            if(root2 == null) return true;            if(root1.val != root2.val) return false;            return DoesTree1HaveTree2(root1.left, root2.left) && DoesTree1HaveTree2(root1.right, root2.right);        }}