【二叉树】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 = DoesTree1HasTree2(root1,root2);
             }
             
            //递归遍历左子树 
            if(!result){
                result = HasSubtree(root1.left, root2);
            }
            
            //递归遍历右子树
            if(!result){
                result = HasSubtree(root1.right, root2);
            }
         }
        
        return result;
    
    }
    
    
    public boolean DoesTree1HasTree2(TreeNode root1,TreeNode root2){
        
        if(root2 == null){
            return true;
        }
        
        if(root1 == null){
            return false;
        }
        
        if(root1.val != root2.val){
            return false;
        }
        
        return DoesTree1HasTree2(root1.left, root2.left) && DoesTree1HasTree2(root1.right, root2.right);
    }
}