输入两棵二叉树A和B，判断B是不是A的子结构。

public class Solution {
    private class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;

        public TreeNode(int val) {
            this.val = val;

        }

    }
    //HasSubtree主要是判断树root1中是否含有root2节点
       public boolean HasSubtree(TreeNode root1,TreeNode root2) {
            if(root2==null) return false;
            if(root1==null && root2!=null) return false;        
            boolean flag = false ;
            if(root1.val==root2.val){
                flag = isSubTree(root1,root2);
            }
            return flag || HasSubtree(root1.left, root2) || HasSubtree(root1.right, root2) ;
        }
      
        private boolean isSubTree(TreeNode root1, TreeNode root2) {
            if(root2==null) return true;
            if(root1==null && root2!=null) return false;        
            if(root1.val==root2.val){
                return isSubTree(root1.left, root2.left) && isSubTree(root1.right, root2.right);
            }
            return false;
        }
    }