检查树是否是二叉搜索树 [英] check if a tree is a binary search tree
问题描述
我编写了以下代码来检查树是否是二进制搜索树。请帮我查一下代码:
I have written the following code to check if a tree is a Binary search tree. Please help me check the code:
好的!代码现在已编辑。这个简单的解决方案是由以下帖子中的人建议的:
Okay! The code is edited now. This simple solution was suggested by someone in the posts below:
IsValidBST(root,-infinity,infinity);
bool IsValidBST(BinaryNode node, int MIN, int MAX)
{
if(node == null)
return true;
if(node.element > MIN
&& node.element < MAX
&& IsValidBST(node.left,MIN,node.element)
&& IsValidBST(node.right,node.element,MAX))
return true;
else
return false;
}
推荐答案
方法只能做一个一次一件事。你做事的方式也很奇怪。
我会给你一些几乎Java伪代码。对不起,但我已经有一段时间没碰过Java了。我希望它有所帮助。看看我在问题上的评论,我希望你把它整理出来!
A Method should only do one thing at a time. Also the way you do things are generally Weird. I will give you some almost-Java pseudocode. Sorry for that, but I have not touched Java for some Time. I hope it helps. Look at the comments I also did on the Question and I hope you sort it out!
像这样打电话给你的isBST:
Call your isBST like that :
public boolean isBst(BNode node)
{
return isBinarySearchTree(node , Integer.MIN_VALUE , Integer.MIN_VALUE);
}
内部:
public boolean isBinarySearchTree(BNode node , int min , int max)
{
if(node.data < min || node.data > max)
return false;
//Check this node!
//This algorithm doesn't recurse with null Arguments.
//When a null is found the method returns true;
//Look and you will find out.
/*
* Checking for Left SubTree
*/
boolean leftIsBst = false;
//If the Left Node Exists
if(node.left != null)
{
//and the Left Data are Smaller than the Node Data
if(node.left.data < node.data)
{
//Check if the subtree is Valid as well
leftIsBst = isBinarySearchTree(node.left , min , node.data);
}else
{
//Else if the Left data are Bigger return false;
leftIsBst = false;
}
}else //if the Left Node Doesn't Exist return true;
{
leftIsBst = true;
}
/*
* Checking for Right SubTree - Similar Logic
*/
boolean rightIsBst = false;
//If the Right Node Exists
if(node.right != null)
{
//and the Right Data are Bigger (or Equal) than the Node Data
if(node.right.data >= node.data)
{
//Check if the subtree is Valid as well
rightIsBst = isBinarySearchTree(node.right , node.data+1 , max);
}else
{
//Else if the Right data are Smaller return false;
rightIsBst = false;
}
}else //if the Right Node Doesn't Exist return true;
{
rightIsBst = true;
}
//if both are true then this means that subtrees are BST too
return (leftIsBst && rightIsBst);
}
现在:如果你想找到 Min
和 Max
您应该使用Container的每个子树的值(我使用 ArrayList
)和存储节点,最小值,最大值
的三元组,它代表根节点和值(显然)。
Now : If you want to find the Min
and Max
Values of each Subtree you should use a Container (I used an ArrayList
) and store a triplet of Node, Min, Max
which represents the root node and the values (obviously).
例如。
/*
* A Class which is used when getting subTrees Values
*/
class TreeValues
{
BNode root; //Which node those values apply for
int Min;
int Max;
TreeValues(BNode _node , _min , _max)
{
root = _node;
Min = _min;
Max = _max;
}
}
并且a:
/*
* Use this as your container to store Min and Max of the whole
*/
ArrayList<TreeValues> myValues = new ArrayList<TreeValues>;
现在这是一个找到 Min
和 Max
给定节点的值:
Now this is a method which finds the Min
and Max
values of a given node:
/*
* Method Used to get Values for one Subtree
* Returns a TreeValues Object containing that (sub-)trees values
*/
public TreeValues GetSubTreeValues(BNode node)
{
//Keep information on the data of the Subtree's Startnode
//We gonna need it later
BNode SubtreeRoot = node;
//The Min value of a BST Tree exists in the leftmost child
//and the Max in the RightMost child
int MinValue = 0;
//If there is not a Left Child
if(node.left == null)
{
//The Min Value is this node's data
MinValue = node.data;
}else
{
//Get me the Leftmost Child
while(node.left != null)
{
node = node.left;
}
MinValue = node.data;
}
//Reset the node to original value
node = SubtreeRoot; //Edit - fix
//Similarly for the Right Child.
if(node.right == null)
{
MaxValue = node.data;
}else
{
int MaxValue = 0;
//Similarly
while(node.right != null)
{
node = node.right;
}
MaxValue = node.data;
}
//Return the info.
return new TreeValues(SubtreeRoot , MinValue , MaxValue);
}
但这只返回一个Node的值,所以我们要用它来查找对于整棵树:
But this returns Values for one Node only, So we gonna use this to find for the Whole Tree:
public void GetTreeValues(BNode node)
{
//Add this node to the Container with Tree Data
myValues.add(GetSubTreeValues(node));
//Get Left Child Values, if it exists ...
if(node.left != null)
GetTreeValues(node.left);
//Similarly.
if(node.right != null)
GetTreeValues(node.right);
//Nothing is returned, we put everything to the myValues container
return;
}
使用此方法,您的通话应该如下所示
Using this methods, your call should look like
if(isBinarySearchTree(root))
GetTreeValues(root);
//else ... Do Something
这几乎是Java。它应该与一些修改和修复工作。找一本好的OO书,它会对你有帮助。请注意,此解决方案可以分解为更多方法。
This is almost Java. It should work with some modification and fix. Find a good OO book, it will help you. Note, that this solution could be broke down into more methods.
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