# What is binary tree and binary search tree

This algorithm is also O n , so it is asymptotically optimal. Traversal can also be implemented iteratively. For certain applications, e. This is, of course, implemented without the callback construct and takes O 1 on average and O log n in the worst case. Sometimes we already have a binary tree, and we need to determine whether it is a BST.

This problem has a simple recursive solution. The BST property—every node on the right subtree has to be larger than the current node and every node on the left subtree has to be smaller than the current node—is the key to figuring out whether a tree is a BST or not. The greedy algorithm —simply traverse the tree, at every node check whether the node contains a value larger than the value at the left child and smaller than the value on the right child—does not work for all cases.

Consider the following tree:. In the tree above, each node meets the condition that the node contains a value larger than its left child and smaller than its right child hold, and yet it is not a BST: Instead of making a decision based solely on the values of a node and its children, we also need information flowing down from the parent as well.

In the case of the tree above, if we could remember about the node containing the value 20, we would see that the node with value 5 is violating the BST property contract. As pointed out in section Traversal , an in-order traversal of a binary search tree returns the nodes sorted. A binary search tree can be used to implement a simple sorting algorithm.

Similar to heapsort , we insert all the values we wish to sort into a new ordered data structure—in this case a binary search tree—and then traverse it in order. There are several schemes for overcoming this flaw with simple binary trees; the most common is the self-balancing binary search tree. If this same procedure is done using such a tree, the overall worst-case time is O n log n , which is asymptotically optimal for a comparison sort.

In practice, the added overhead in time and space for a tree-based sort particularly for node allocation make it inferior to other asymptotically optimal sorts such as heapsort for static list sorting.

On the other hand, it is one of the most efficient methods of incremental sorting , adding items to a list over time while keeping the list sorted at all times. Binary search trees can serve as priority queues: Insertion works as previously explained. Find-min walks the tree, following left pointers as far as it can without hitting a leaf:.

Delete-min max can simply look up the minimum maximum , then delete it. This way, insertion and deletion both take logarithmic time, just as they do in a binary heap , but unlike a binary heap and most other priority queue implementations, a single tree can support all of find-min , find-max , delete-min and delete-max at the same time, making binary search trees suitable as double-ended priority queues.

There are many types of binary search trees. AVL trees and red-black trees are both forms of self-balancing binary search trees. A splay tree is a binary search tree that automatically moves frequently accessed elements nearer to the root. In a treap tree heap , each node also holds a randomly chosen priority and the parent node has higher priority than its children. Tango trees are trees optimized for fast searches.

T-trees are binary search trees optimized to reduce storage space overhead, widely used for in-memory databases. A degenerate tree is a tree where for each parent node, there is only one associated child node. It is unbalanced and, in the worst case, performance degrades to that of a linked list. If your add node function does not handle re-balancing, then you can easily construct a degenerate tree by feeding it with data that is already sorted.

What this means is that in a performance measurement, the tree will essentially behave like a linked list data structure. Heger [4] presented a performance comparison of binary search trees.

Treap was found to have the best average performance, while red-black tree was found to have the smallest amount of performance variations. If we do not plan on modifying a search tree, and we know exactly how often each item will be accessed, we can construct [5] an optimal binary search tree , which is a search tree where the average cost of looking up an item the expected search cost is minimized.

Even if we only have estimates of the search costs, such a system can considerably speed up lookups on average. For example, if you have a BST of English words used in a spell checker , you might balance the tree based on word frequency in text corpora , placing words like the near the root and words like agerasia near the leaves. Such a tree might be compared with Huffman trees , which similarly seek to place frequently used items near the root in order to produce a dense information encoding; however, Huffman trees store data elements only in leaves, and these elements need not be ordered.

If we do not know the sequence in which the elements in the tree will be accessed in advance, we can use splay trees which are asymptotically as good as any static search tree we can construct for any particular sequence of lookup operations. Alphabetic trees are Huffman trees with the additional constraint on order, or, equivalently, search trees with the modification that all elements are stored in the leaves.

Faster algorithms exist for optimal alphabetic binary trees OABTs. From Wikipedia, the free encyclopedia. Binary search tree Type tree Invented Invented by P. Optimal binary search tree. Let a random BST be one built using only insertions out of a sequence of unique elements in random order all permutations equally likely ; then the expected height of the tree is O log n. If deletions are allowed as well as insertions, "little is known about the average height of a binary search tree".

Introduction to Algorithms 3rd ed. Robert Sedgewick , Kevin Wayne: Algorithms and Data Structures: Archived from the original on 12 October Retrieved 1 December Binary decision diagram Directed acyclic graph Directed acyclic word graph. List of data structures. Retrieved from " https: Binary trees Data types Search trees. Views Read Edit View history. In other projects Wikimedia Commons. This page was last edited on 17 April , at Another way to explain insertion is that in order to insert a new node in the tree, its key is first compared with that of the root.

If its key is less than the root's, it is then compared with the key of the root's left child. If its key is greater, it is compared with the root's right child. This process continues, until the new node is compared with a leaf node, and then it is added as this node's right or left child, depending on its key: There are other ways of inserting nodes into a binary tree, but this is the only way of inserting nodes at the leaves and at the same time preserving the BST structure. When removing a node from a binary search tree it is mandatory to maintain the in-order sequence of the nodes.

There are many possibilities to do this. However, the following method which has been proposed by T. Hibbard in [2] guarantees that the heights of the subject subtrees are changed by at most one.

There are three possible cases to consider:. Broadly speaking, nodes with children are harder to delete. As with all binary trees, a node's in-order successor is its right subtree's left-most child, and a node's in-order predecessor is the left subtree's right-most child.

In either case, this node will have only one or no child at all. Delete it according to one of the two simpler cases above. Consistently using the in-order successor or the in-order predecessor for every instance of the two-child case can lead to an unbalanced tree, so some implementations select one or the other at different times.

Although this operation does not always traverse the tree down to a leaf, this is always a possibility; thus in the worst case it requires time proportional to the height of the tree. It does not require more even when the node has two children, since it still follows a single path and does not visit any node twice.

Once the binary search tree has been created, its elements can be retrieved in-order by recursively traversing the left subtree of the root node, accessing the node itself, then recursively traversing the right subtree of the node, continuing this pattern with each node in the tree as it's recursively accessed. As with all binary trees, one may conduct a pre-order traversal or a post-order traversal , but neither are likely to be useful for binary search trees.

An in-order traversal of a binary search tree will always result in a sorted list of node items numbers, strings or other comparable items. The code for in-order traversal in Python is given below. It will call callback some function the programmer wishes to call on the node's value, such as printing to the screen for every node in the tree. Traversal requires O n time, since it must visit every node. This algorithm is also O n , so it is asymptotically optimal.

Traversal can also be implemented iteratively. For certain applications, e. This is, of course, implemented without the callback construct and takes O 1 on average and O log n in the worst case. Sometimes we already have a binary tree, and we need to determine whether it is a BST. This problem has a simple recursive solution. The BST property—every node on the right subtree has to be larger than the current node and every node on the left subtree has to be smaller than the current node—is the key to figuring out whether a tree is a BST or not.

The greedy algorithm —simply traverse the tree, at every node check whether the node contains a value larger than the value at the left child and smaller than the value on the right child—does not work for all cases. Consider the following tree:. In the tree above, each node meets the condition that the node contains a value larger than its left child and smaller than its right child hold, and yet it is not a BST: Instead of making a decision based solely on the values of a node and its children, we also need information flowing down from the parent as well.

In the case of the tree above, if we could remember about the node containing the value 20, we would see that the node with value 5 is violating the BST property contract.

As pointed out in section Traversal , an in-order traversal of a binary search tree returns the nodes sorted. A binary search tree can be used to implement a simple sorting algorithm. Similar to heapsort , we insert all the values we wish to sort into a new ordered data structure—in this case a binary search tree—and then traverse it in order.

There are several schemes for overcoming this flaw with simple binary trees; the most common is the self-balancing binary search tree. If this same procedure is done using such a tree, the overall worst-case time is O n log n , which is asymptotically optimal for a comparison sort. In practice, the added overhead in time and space for a tree-based sort particularly for node allocation make it inferior to other asymptotically optimal sorts such as heapsort for static list sorting.

On the other hand, it is one of the most efficient methods of incremental sorting , adding items to a list over time while keeping the list sorted at all times. Binary search trees can serve as priority queues: Insertion works as previously explained. Find-min walks the tree, following left pointers as far as it can without hitting a leaf:. Delete-min max can simply look up the minimum maximum , then delete it.

This way, insertion and deletion both take logarithmic time, just as they do in a binary heap , but unlike a binary heap and most other priority queue implementations, a single tree can support all of find-min , find-max , delete-min and delete-max at the same time, making binary search trees suitable as double-ended priority queues.

There are many types of binary search trees. AVL trees and red-black trees are both forms of self-balancing binary search trees. A splay tree is a binary search tree that automatically moves frequently accessed elements nearer to the root. In a treap tree heap , each node also holds a randomly chosen priority and the parent node has higher priority than its children. Tango trees are trees optimized for fast searches. T-trees are binary search trees optimized to reduce storage space overhead, widely used for in-memory databases.

A degenerate tree is a tree where for each parent node, there is only one associated child node. It is unbalanced and, in the worst case, performance degrades to that of a linked list. If your add node function does not handle re-balancing, then you can easily construct a degenerate tree by feeding it with data that is already sorted. What this means is that in a performance measurement, the tree will essentially behave like a linked list data structure.

Heger [4] presented a performance comparison of binary search trees. Treap was found to have the best average performance, while red-black tree was found to have the smallest amount of performance variations. If we do not plan on modifying a search tree, and we know exactly how often each item will be accessed, we can construct [5] an optimal binary search tree , which is a search tree where the average cost of looking up an item the expected search cost is minimized.