面试题26：数的子结构 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 ShuDeZiJieGou {
    public boolean HasSubtree(TreeNode root1,TreeNode root2) {
         boolean result = false;
        if(root2==null){
            return false;
        }
        if(root1==null){
            return false;
        }
        if(root1.val == root2.val)
            result = tree1HaveTree2(root1,root2);
        if(!result)
            result=HasSubtree(root1.left,root2);
        if(!result)
            result=HasSubtree(root1.right,root2);
        return result;
    }
    public boolean tree1HaveTree2(TreeNode root1,TreeNode root2){
        boolean result = false;
        //先判断让root2是否为null
        if(root2==null){
            return true;
        }
        
        if(root1==null){
            return false;
        }
                
        if(root1.val != root2.val){
            return false;
        }
                
        return (tree1HaveTree2(root1.left,root2.left) &&
                tree1HaveTree2(root1.right,root2.right));
        }
}