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tidied up code based on error reports by clang-tidy
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Krishna Vedala
parent
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commit
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@ -1,241 +1,235 @@
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/**
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* @file skip_list.cpp
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* @brief Data structure for fast searching and insertion in \f$O(\log n)\f$ time
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* @brief Data structure for fast searching and insertion in \f$O(\log n)\f$
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* time
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* @details
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* A skip list is a data structure that is used for storing a sorted list of items with a
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* help of hierarchy of linked lists that connect increasingly sparse subsequences of the items
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* A skip list is a data structure that is used for storing a sorted list of
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* items with a help of hierarchy of linked lists that connect increasingly
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* sparse subsequences of the items
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*
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* References used: [GeeksForGeek](https://www.geeksforgeeks.org/skip-list/), [OpenGenus](https://iq.opengenus.org/skip-list) for PseudoCode and Code
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* References used: [GeeksForGeek](https://www.geeksforgeeks.org/skip-list/),
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* [OpenGenus](https://iq.opengenus.org/skip-list) for PseudoCode and Code
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* @author [enqidu](https://github.com/enqidu)
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* .
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*/
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* @author [Krishna Vedala](https://github.com/kvedala)
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*/
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#include <iostream>
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#include <vector>
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#include <array>
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#include <cstring>
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#include <ctime>
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#include <iostream>
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#include <memory>
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#include <vector>
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using std::vector;
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using std::endl;
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#define MAX_LEVEL 2 ///< Maximum level of skip list
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#define PROBABILITY 0.5 ///< Current probability for "coin toss"
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/** \namespace data_structure
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* \brief Data-structure algorithms
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*/
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namespace data_structure {
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constexpr int MAX_LEVEL = 2; ///< Maximum level of skip list
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constexpr float PROBABILITY = 0.5; ///< Current probability for "coin toss"
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/**
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* Node structure [Key][Node*, Node*...]
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*/
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*/
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struct Node {
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int key; ///< key integer
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int key; ///< key integer
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void* value; ///< pointer of value
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vector<Node*> forward; ///< nodes of the given one in all levels
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// Constructor of the node
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Node(int key, int level, void* value);
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};
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std::vector<std::shared_ptr<Node>>
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forward; ///< nodes of the given one in all levels
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/**
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* Creates node with provided key, level and value
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* @param key is number that is used for comparision
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* @param level is the maximum level node's going to added
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*/
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Node::Node(int key, int level, void* value) {
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this->key = key;
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//Initialization of forward vector
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for (int i = 0; i < (level+1); i++){
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forward.push_back(nullptr);
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/**
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* Creates node with provided key, level and value
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* @param key is number that is used for comparision
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* @param level is the maximum level node's going to added
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*/
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Node(int key, int level, void* value = nullptr) : key(key) {
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// Initialization of forward vector
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for (int i = 0; i < (level + 1); i++) {
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forward.push_back(nullptr);
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}
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}
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}
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};
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/**
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* SkipList class implementation with basic methods
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*/
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*/
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class SkipList {
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int level; ///< Maximum level of the skiplist
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Node *header; ///< Pointer to the header node
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public:
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SkipList();
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int randomLevel();
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void insertElement(int, void*);
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void deleteElement(int);
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void* searchElement(int);
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void displayList();
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~SkipList();
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int level; ///< Maximum level of the skiplist
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std::shared_ptr<Node> header; ///< Pointer to the header node
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public:
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/**
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* Skip List constructor. Initializes header, start
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* Node for searching in the list
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*/
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SkipList() {
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level = 0;
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// Header initialization
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header = std::shared_ptr<Node>(new Node(-1, MAX_LEVEL));
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}
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/**
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* Destructor for skiplist class
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*/
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~SkipList() {
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for (int i = 0; i <= level; i++) {
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std::shared_ptr<Node> node = header->forward[i];
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std::shared_ptr<Node> temp;
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while (node != nullptr) {
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temp = node;
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node = node->forward[i];
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temp.reset();
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}
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}
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header.reset();
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}
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/**
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* Returns random level of the skip list.
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* Every higher level is 2 times less likely.
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* @return random level for skip list
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*/
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int randomLevel() {
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int lvl = 0;
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while (static_cast<float>(std::rand() / RAND_MAX) < PROBABILITY &&
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lvl < MAX_LEVEL)
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lvl++;
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return lvl;
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}
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/**
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* Inserts elements with given key and value;
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* It's level is computed by randomLevel() function.
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* @param key is number that is used for comparision
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* @param value pointer to a value, that can be any type
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*/
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void insertElement(int key, void* value) {
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std::cout << "Inserting" << key << "...";
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std::shared_ptr<Node> x = header;
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std::array<std::shared_ptr<Node>, MAX_LEVEL + 1> update;
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update.fill(nullptr);
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for (int i = level; i >= 0; i--) {
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while (x->forward[i] != nullptr && x->forward[i]->key < key)
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x = x->forward[i];
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update[i] = x;
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}
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x = x->forward[0];
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bool doesnt_exist = (x == nullptr || x->key != key);
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if (doesnt_exist) {
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int rlevel = randomLevel();
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if (rlevel > level) {
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for (int i = level + 1; i < rlevel + 1; i++) update[i] = header;
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// Update current level
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level = rlevel;
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}
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std::shared_ptr<Node> n =
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std::shared_ptr<Node>(new Node(key, rlevel, value));
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for (int i = 0; i <= rlevel; i++) {
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n->forward[i] = update[i]->forward[i];
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update[i]->forward[i] = n;
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}
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std::cout << "Inserted" << std::endl;
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} else {
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std::cout << "Exists" << std::endl;
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}
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}
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/**
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* Deletes an element by key and prints if has been removed successfully
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* @param key is number that is used for comparision.
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*/
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void deleteElement(int key) {
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std::shared_ptr<Node> x = header;
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std::array<std::shared_ptr<Node>, MAX_LEVEL + 1> update;
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update.fill(nullptr);
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for (int i = level; i >= 0; i--) {
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while (x->forward[i] != nullptr && x->forward[i]->key < key)
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x = x->forward[i];
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update[i] = x;
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}
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x = x->forward[0];
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bool doesnt_exist = (x == nullptr || x->key != key);
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if (!doesnt_exist) {
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for (int i = 0; i <= level; i++) {
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if (update[i]->forward[i] != x)
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break;
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update[i]->forward[i] = x->forward[i];
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}
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/* Remove empty levels*/
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while (level > 0 && header->forward[level] == nullptr) level--;
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std::cout << "Deleted" << std::endl;
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} else {
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std::cout << "Doesn't exist" << std::endl;
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}
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}
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/**
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* Searching element in skip list structure
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* @param key is number that is used for comparision
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* @return pointer to the value of the node
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*/
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void* searchElement(int key) {
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std::shared_ptr<Node> x = header;
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std::cout << "Searching for " << key << std::endl;
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for (int i = level; i >= 0; i--) {
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while (x->forward[i] && x->forward[i]->key < key) x = x->forward[i];
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}
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x = x->forward[0];
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if (x && x->key == key) {
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std::cout << "Found" << std::endl;
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return x->value;
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} else {
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std::cout << "Not Found" << std::endl;
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return nullptr;
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}
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}
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/*
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* Display skip list level
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*/
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void displayList() {
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std::cout << "Displaying list:\n" << std::endl;
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for (int i = 0; i <= level; i++) {
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std::shared_ptr<Node> node = header->forward[i];
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std::cout << "Level " << (i) << ": ";
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while (node != nullptr) {
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std::cout << node->key << " ";
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node = node->forward[i];
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}
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std::cout << std::endl;
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}
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}
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};
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/**
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* Skeep List constructor. Initializes header, start
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* Node for searching in the list
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*/
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SkipList::SkipList() {
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level = 0;
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// Header initialization
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header = new Node(-1, MAX_LEVEL, nullptr);
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}
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/**
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* Destructor for skiplist class
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*/
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SkipList::~SkipList(){
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for(int i=0; i <= level; i++) {
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Node *node = header->forward[i];
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Node* temp;
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while(node != nullptr) {
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temp = node;
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node = node->forward[i];
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delete temp;
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}
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}
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delete header;
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}
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/**
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* Returns random level of the skip list.
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* Every higher level is 2 times less likely.
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* @return lvl: random level for skip list;
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*/
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int SkipList::randomLevel() {
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int lvl = 0;
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while(static_cast<float>(std::rand())/RAND_MAX < PROBABILITY && lvl < MAX_LEVEL) lvl++;
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return lvl;
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}
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/**
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* Inserts elements with given key and value;
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* It's level is computed by randomLevel() function.
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* @param key is number that is used for comparision
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* @param value pointer to a value, that can be any type
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*/
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void SkipList::insertElement(int key, void* value) {
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std::cout << "Inserting" << key << "...";
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Node *x = header;
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Node *update[MAX_LEVEL+1];
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memset(update, 0, sizeof(Node*)*(MAX_LEVEL+1));
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for(int i = level; i >= 0; i--) {
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while(x->forward[i] != nullptr && x->forward[i]->key < key) x = x->forward[i];
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update[i] = x;
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}
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x = x->forward[0];
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bool doesnt_exist = (x == nullptr || x->key != key);
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if (doesnt_exist) {
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int rlevel = randomLevel();
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if(rlevel > level) {
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for(int i=level+1;i<rlevel+1;i++) update[i] = header;
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// Update current level
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level = rlevel;
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}
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Node* n = new Node(key, rlevel, value);
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for(int i=0;i<=rlevel;i++) {
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n->forward[i] = update[i]->forward[i];
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update[i]->forward[i] = n;
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}
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std::cout << "Inserted" << endl;
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} else {
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std::cout << "Exists" << endl;
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}
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}
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/**
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* Deletes an element by key and prints if has been removed successfully
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* @param key is number that is used for comparision.
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*/
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void SkipList::deleteElement(int key) {
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Node *x = header;
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Node *update[MAX_LEVEL+1];
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memset(update, 0, sizeof(Node*)*(MAX_LEVEL+1));
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for(int i = level; i >= 0; i--) {
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while(x->forward[i] != nullptr && x->forward[i]->key < key) x = x->forward[i];
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update[i] = x;
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}
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x = x->forward[0];
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bool doesnt_exist = (x == nullptr || x->key != key);
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if(!doesnt_exist) {
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for(int i=0;i<=level;i++) {
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if(update[i]->forward[i] != x) break;
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update[i]->forward[i] = x->forward[i];
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}
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/* Remove empty levels*/
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while(level>0 && header->forward[level] == 0) level--;
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std::cout << "Deleted" << endl;
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} else {
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std::cout << "Doesn't exist" << endl;
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}
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}
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/**
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* Searching element in skip list structure
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* @param key is number that is used for comparision
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* @return pointer to the value of the node
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*/
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void* SkipList::searchElement(int key) {
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Node *x = header;
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std::cout << "Searching for " + key << endl;
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for(int i = level; i >= 0; i--) {
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while(x->forward[i] && x->forward[i]->key < key) x = x->forward[i];
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}
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x = x->forward[0];
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if(x && x->key == key){
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std::cout << "Found" << endl;
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return x->value;
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} else {
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std::cout << "Not Found" << endl;
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return nullptr;
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}
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}
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/*
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* Display skip list level
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*/
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void SkipList::displayList() {
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std::cout << "Displaying list:\n" << endl;
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for(int i=0; i <= level; i++) {
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Node *node = header->forward[i];
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std::cout << "Level " << (i) << ": ";
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while(node != nullptr) {
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std::cout << node->key << " ";
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node = node->forward[i];
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}
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std::cout << endl;
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}
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}
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} // namespace data_structure
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/**
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* Main function:
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* Creates and inserts random 2^[number of levels]
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* elements into the skip lists and than displays it
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*/
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int main()
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{
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int main() {
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std::srand(std::time(nullptr));
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SkipList lst;
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data_structure::SkipList lst;
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for (int j = 0; j < (1 << (MAX_LEVEL+1)); j++){
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int k = (std::rand()%( 1 << (MAX_LEVEL+2)) + 1);
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lst.insertElement(k, &j);
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for (int j = 0; j < (1 << (data_structure::MAX_LEVEL + 1)); j++) {
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int k = (std::rand() % (1 << (data_structure::MAX_LEVEL + 2)) + 1);
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lst.insertElement(k, &j);
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}
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lst.displayList();
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}
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