update

README.md

@@ -179,6 +179,21 @@ A data structure is a data organization, management, and storage format that is
 </tbody>
 </table>
 
+**Advanced Data Structures and Algorithms**
+
+<table>
+<thead>
+<th>Advanced Concept</th>
+<th>Programming Languages</th>
+</thead>
+<tbody>
+<tr>
+<td>Skiplist</td>
+<td>
+</td>
+</tr>
+</tbody>
+</table>
 ## 🔆 Collections
 
 **Competitive Programming Events**

problems/skiplist/src/BUILD

@@ -1,5 +1,8 @@
+load("@rules_cc//cc:defs.bzl", "cc_binary")
+
 cc_binary(
     name = "skiplist",
     srcs = ["skiplist.cpp", "skiplist.h"],
+    copts = ["-std=c++17", "-Wall", "-Wextra", "-Werror"],
     deps = [],
 )

problems/skiplist/src/skiplist.cpp

@@ -3,50 +3,28 @@
 
 using namespace std;
 
-// add class Class 
-class Class {
-public:
-  int id;
-  string name;
-  Class(int id, string name) {
-    this->id = id;
-    this->name = name;
-  }
-};
-
-class Student {
-public:
-  int id;
-  string name;
-  Class* classes[10];
-
-  Student(int id, string name) {
-    this->id = id;
-    this->name = name;
-  }
-
-  void addClass(Class* c) {
-
-    for (int i = 0; i < 10; i++) {
-      if (classes[i] == NULL) {
-        classes[i] = c;
-        break;
-      }
-    }
-  }
-};
-
 int main(){
   cout << "Skiplist Program" << endl;
 
   // create an skiplist
   Skiplist sl;
-  // // insert 3 elements
+
+  cout << "\nInsert elements into Skiplist" << endl;
   sl.insert(4);
   sl.insert(2);
   sl.insert(3);
-  sl.insert(8);
+  sl.insert(9);
   sl.insert(1);
   sl.show();
+
+  cout << "\nSearch elements" << endl;
+  cout << "- Search for 3: " << sl.search(3) << endl;
+  cout << "- Search for 5: " << sl.search(5) << endl;
+
+  cout << "\nRemove elements" << endl;
+  sl.remove(3);
+  sl.remove(5);  
+  sl.show();
+
   return 0;
 }

problems/skiplist/src/skiplist.h

@@ -1,114 +1,123 @@
-#include <iostream>
 #include <climits>
+#include <iostream>
 
 using namespace std;
 
-// create class Skiplist
-
-// Node struct
 struct Node {
   int key;
   int level;
   Node** forwards;
   // constructor
-  Node(int key, int level){
+  Node(int key, int level) {
     this->key = key;
     this->level = level;
-    forwards = new Node*[level+1];
-    for(int i=0; i<=level; i++){
+    forwards = new Node*[level + 1];
+    for (int i = 0; i <= level; i++) {
       forwards[i] = NULL;
     }
   }
 };
 
 class Skiplist {
-  public:
-    Skiplist();
-    ~Skiplist();
-    void insert(int key);
-    void insert2(int key);
-    bool search(int key);
-    void erase(int key);
-    void show();
-  private:
-    Node* head;
-    int MAX_LEVEL;
+ public:
+  Skiplist(int max_level);
+  ~Skiplist();
+  void insert(int key);
+  bool search(int key);
+  void remove(int key);
+  void show();
+
+ private:
+  Node* head;
+  int MAX_LEVEL;
 };
 
-Skiplist::Skiplist(){
-  MAX_LEVEL = 16;
+Skiplist::Skiplist(int max_level = 4): MAX_LEVEL(max_level) {
   head = new Node(INT_MIN, MAX_LEVEL);
   srand(time(NULL));
 }
 
-Skiplist::~Skiplist(){
-  delete head;
-}
+Skiplist::~Skiplist() { delete head; }
 
-void Skiplist::insert(int key){
-  // Create a new node with the given key.
-  // The level of the new node is a random number between 0 and MAX_LEVEL
-  // create random number between 0 to 1, if < 0.5, level++; otherwise, break
+void Skiplist::insert(int key) {
   int level = 0;
-
-  while(rand() % 2 && level < MAX_LEVEL){
+  while (rand() % 2 && level < MAX_LEVEL) {
     level++;
   }
   Node* newNode = new Node(key, level);
-  // print newNode key and level
-  cout << "newNode (" << newNode->key << ", " << newNode->level << ")" << endl;
-
-  // Create a pointer to the current node
+
   Node* current = head;
-  // Create an array of pointers to the previous nodes
-  // with size equal to the random level
-  Node** update = new Node*[level+1];
-  for(int i=0; i<=level; i++){
+  Node** update = new Node*[level + 1];
+  for (int i = 0; i <= level; i++) {
     update[i] = NULL;
   }
 
-  // // Traverse the list from the highest level to the lowest level
-  // // and find the previous node for each level
-  for(int i=level; i>=0; i--){
-    while(current->forwards[i] != NULL && current->forwards[i]->key < key){
-      // update the curent node
+  for (int i = level; i >= 0; i--) {
+    while (current->forwards[i] != NULL && current->forwards[i]->key < key) {
       current = current->forwards[i];
     }
-    // update the previous node for the current level
     update[i] = current;
   }
 
-  // cout << "Debug" << endl;
-
-  // // Set the next node for the new node to the next node of the previous node
-  // // for the lowest level
-  newNode->forwards[0] = update[0]->forwards[0];
-  // // Set the next node of the previous node for the lowest level to the new node
-  update[0]->forwards[0] = newNode;
-
-  for(int i=1; i<=level; i++){
+  for (int i = 0; i <= level; i++) {
     newNode->forwards[i] = update[i]->forwards[i];
     update[i]->forwards[i] = newNode;
-  } 
+  }
+}
+
+bool Skiplist::search(int key) {
+  Node* current = head;
+  for (int i = MAX_LEVEL; i >= 0; i--) {
+    while (current->forwards[i] != NULL && current->forwards[i]->key < key) {
+      current = current->forwards[i];
+    }
+  }
+  if (current->forwards[0] != NULL && current->forwards[0]->key == key) {
+    return true;
+  }
+  return false;
 }
 
-// show skiplist of all levels
-// level 0 will have all elements
-// if an element is not exist in a level, print " "
-void Skiplist::show(){
-  cout << "Skiplist::show" << endl;
+void Skiplist::remove(int key) {
+  Node* current = head;
+  Node** update = new Node*[MAX_LEVEL + 1];
+  for (int i = 0; i <= MAX_LEVEL; i++) {
+    update[i] = NULL;
+  }
+
+  for (int i = MAX_LEVEL; i >= 0; i--) {
+    while (current->forwards[i] != NULL && current->forwards[i]->key < key) {
+      current = current->forwards[i];
+    }
+    update[i] = current;
+  }
+
+  current = current->forwards[0];
+
+  if (current && current->key == key) {
+    for (int i = 0; i <= MAX_LEVEL; i++) {
+      if (update[i]->forwards[i] != current) {
+        break;
+      }
+      update[i]->forwards[i] = current->forwards[i];
+    }
+    delete current;
+  }
+  delete[] update;
+}
 
+void Skiplist::show() {
   Node* current = head;
-  while(current->forwards[0] != NULL){
+  while (current->forwards[0] != NULL) {
     cout << current->forwards[0]->key << " ";
     current = current->forwards[0];
   }
+  cout << endl;
 
-  // show for each levels
-  for(int i=MAX_LEVEL; i>=0; i--){
+  for (int i = MAX_LEVEL; i >= 0; i--) {
     cout << "Level " << i << ": ";
     Node* current = head;
-    while(current->forwards[i] != NULL){
+    while (current->forwards[i] != NULL) {
       cout << current->forwards[i]->key << " -> ";
       current = current->forwards[i];
     }