C program for binary search
4 stars based on
In computinga persistent data structure is a data structure that always preserves the previous version of itself when it is modified. Such data structures are effectively immutableas their operations do not visibly update the structure in-place, but instead always yield a new updated structure.
The term was introduced in Driscoll, Sarnak, Sleator, and Tarjans' article . A data structure is partially persistent if all versions can be accessed but only the newest copy binary tree c program can be modified.
The data structure is fully persistent if every version can be both accessed and modified. If there is also a meld or merge operation that can create a new version from two previous versions, the data structure is called confluently persistent. Structures that are not persistent are called ephemeral. Copy binary tree c program types of data structures are particularly common in logical and functional programmingand in a purely functional program all data is immutable, so all data structures are automatically fully persistent.
Purely functional data structures are persistent data structures that completely avoid the use of mutable state, but can often still achieve attractive amortized time complexity bounds.
While persistence can be achieved by simple copying, this is inefficient in CPU and RAM usage, because most operations make only small changes to a data structure. A better method is to exploit the similarity between the copy binary tree c program and old versions to share structure between them, such as using the same subtree in a number of tree structures.
However, because it rapidly becomes infeasible to determine how many previous versions share which parts of the structure, and because it is often desirable to discard old versions, this necessitates an environment with garbage collection.
However, it is not so infeasible that a sophisticated project, such as the ZFS copy-on-write file system, is unable to achieve this by tracking storage allocation directly. In the partial persistence model, we may query any previous version of the data structure, but we may only update the latest version.
This implies a linear ordering among the versions. Three methods on balanced binary search tree: Fat node method is to record all changes made to node fields in the nodes themselves, without erasing old values of the fields. In other words, each fat node contains the same information and pointer fields as an ephemeral node, along with space for an arbitrary number of extra field values.
Each extra field value has an associated field name and a version stamp which indicates the version in which the named field was changed to have the specified value.
Besides, each fat node copy binary tree c program its own version stamp, indicating the version in which the node was created. The only purpose of nodes having version stamps is to make sure that each node only contains one value per field name per version.
In order to navigate through the structure, each original field value in a node has a version stamp of zero. With using fat node method, it requires O 1 space for every modification: Each modification takes O 1 additional time to store the modification at the end of the modification history.
This is an amortized time bound, assuming we store the modification history in a growable array. For access timewe must find the right version at each node as we traverse the structure. If we made m modifications, then each access operation has O log m slowdown resulting from the cost of finding the nearest modification in the array. Path copy is to make a copy of all nodes copy binary tree c program the path which contains the node we are about to insert or delete.
Then we must cascade the change back through the data structure: These modifications cause more cascading changes, and so on, until we reach to the root. We maintain an array of roots indexed by timestamp.
With m modifications, this costs O log m additive lookup time. Modification time and space are bounded by the size of the structure, since a single modification may cause the entire structure to be copied.
SleatorTarjan et al. In each node, we store one modification box. Whenever we access a node, we check the modification box, and compare its timestamp against the access time. The access time specifies the version of the data structure that we care about. If the modification box is empty, or the access time is before the modification time, then we ignore the modification box and just copy binary tree c program with the normal part of the node.
On the other hand, if copy binary tree c program access time is after the modification time, then we use the value in the modification box, overriding that value copy binary tree c program the node.
Say the modification box has a new left pointer. Modifying a node works like this. We assume that each modification touches one pointer or similar field. Otherwise, the modification box is full. We make a copy of copy binary tree c program node, but using only the latest values. Then we perform the modification directly on the new node, without using the modification box. With copy binary tree c program algorithmgiven any time t, at most one modification box exists in the data structure with time t.
Thus, a modification at time t splits the tree into three parts: Time and space for modifications require amortized analysis. A modification takes O 1 amortized space, and O 1 amortized time. The live nodes of T are just the nodes that are reachable from the current root at the current time that is, after the last modification. The full live nodes are the live nodes whose modification boxes are full.
Each modification involves some number of copies, say k, followed by 1 change to a modification box. Consider each of the k copies. Each costs O 1 space and time, but decreases the potential function by one. First, the node we copy must be full and live, so it contributes to the potential function. In fully persistent model, both updates and queries are allowed on any version of the data structure. In confluently persistent model, we use combinators to combine input of more than one previous version to output a new single version.
Rather than a branching tree, combinations of versions induce a DAG directed acyclic graph structure on the version graph.
Perhaps the simplest persistent data structure is the singly linked list or cons -based list, a simple list of objects formed by each carrying a reference to the next in the list. This is persistent because we can take a tail of the list, meaning the last k items for some kand add new nodes on to the front of it. The tail will not be duplicated, instead becoming shared between both the old list and the new list.
So long as the contents of the tail are immutable, this sharing will be copy binary tree c program to the program. Many common reference-based data structures, such as red—black trees stacks and treaps can easily be adapted to create a persistent version.
Some others need slightly more effort, for example: There also exist persistent data structures which copy binary tree c program destructive [ clarification needed ] operations, making them impossible to implement efficiently in purely functional languages like Haskell outside specialized monads like state or IObut possible in languages like C or Java.
These types of data structures can often be avoided with a different design. One primary advantage to using purely persistent data structures is that they often behave better in multi-threaded environments. Singly linked lists are the bread-and-butter data structure in functional languages. In ML -derived languages and Haskellthey are purely functional because once a node copy binary tree c program the list has been allocated, it cannot be modified, only copied or destroyed.
Note that ML itself is not purely functional. Notice that the nodes in list xs have been copied, but the nodes in ys are shared. As a result, the original lists xs and ys persist and have not been modified.
The reason for the copy is that the last node in xs the node containing the original value 2 cannot be modified to point to the start of ysbecause that would change the value of xs.
Consider a binary tree used for fast searchingwhere every node has the recursive invariant that subnodes on the left are less than the node, and subnodes on the right are greater than the node. Firstly the original tree xs persists. Secondly many common nodes are copy binary tree c program between the old tree and the new tree. Such persistence and sharing is difficult to manage without some form of garbage collection GC to automatically free up nodes which have no live references, and this is why GC is a feature commonly found in functional programming languages.
Since every value in a purely functional computation is built up out of existing values, it would seem that it is impossible copy binary tree c program create a cycle of references. In that case, the reference graph the graph of the references from object to object could only be a directed acyclic graph.
However, in most functional languages, functions can be defined recursively ; this capability allows recursive structures using functional suspensions. In lazy languages, such as Haskellall data structures are represented as implicitly suspended thunks ; in these languages any data structure can be recursive because a value can be defined in terms of itself.
Some other languages, such as OCamlallow the explicit definition of recursive values. From Wikipedia, the free encyclopedia. Not to be confused with persistent storage.