Add skiplist.cpp

skiplist.cpp

@@ -0,0 +1,118 @@
+#include <iostream>
+#include <cstdlib>
+
+class SkipNode {
+public:
+    int key;
+    SkipNode** forward;
+
+    SkipNode(int k, int level) : key(k) {
+        forward = new SkipNode*[level + 1];
+        for (int i = 0; i <= level; ++i) {
+            forward[i] = nullptr;
+        }
+    }
+
+    ~SkipNode() {
+        delete[] forward;
+    }
+};
+
+class SkipList {
+public:
+    SkipList(int maxLevels, float probability) : MAX_LEVELS(maxLevels), probability(probability) {
+        level = 0;
+        header = new SkipNode(-1, MAX_LEVELS);
+    }
+
+    ~SkipList() {
+        delete header;
+    }
+
+    // Generate a random level for a new node
+    int randomLevel() {
+        int lvl = 0;
+        while (static_cast<float>(rand()) / RAND_MAX < probability && lvl < MAX_LEVELS) {
+            lvl++;
+        }
+        return lvl;
+    }
+
+    // Insert a key into the Skip List
+    void insert(int key) {
+        SkipNode* update[MAX_LEVELS + 1];
+        SkipNode* current = header;
+
+        for (int i = level; i >= 0; i--) {
+            while (current->forward[i] != nullptr && current->forward[i]->key < key) {
+                current = current->forward[i];
+            }
+            update[i] = current;
+        }
+
+        current = current->forward[0];
+
+        if (current == nullptr || current->key != key) {
+            int newLevel = randomLevel();
+            if (newLevel > level) {
+                for (int i = level + 1; i <= newLevel; i++) {
+                    update[i] = header;
+                }
+                level = newLevel;
+            }
+
+            SkipNode* newNode = new SkipNode(key, newLevel);
+
+            for (int i = 0; i <= newLevel; i++) {
+                newNode->forward[i] = update[i]->forward[i];
+                update[i]->forward[i] = newNode;
+            }
+        }
+    }
+
+    // Search for a key in the Skip List
+    bool search(int key) {
+        SkipNode* current = header;
+        for (int i = level; i >= 0; i--) {
+            while (current->forward[i] != nullptr && current->forward[i]->key < key) {
+                current = current->forward[i];
+            }
+        }
+        current = current->forward[0];
+        return (current != nullptr && current->key == key);
+    }
+
+    void display() {
+        for (int i = 0; i <= level; i++) {
+            SkipNode* node = header->forward[i];
+            std::cout << "Level " << i << ": ";
+            while (node != nullptr) {
+                std::cout << node->key << " ";
+                node = node->forward[i];
+            }
+            std::cout << std::endl;
+        }
+    }
+
+private:
+    const int MAX_LEVELS;
+    const float probability;
+    int level;
+    SkipNode* header;
+};
+
+int main() {
+    SkipList skipList(4, 0.5); // Max levels and probability
+
+    skipList.insert(10);
+    skipList.insert(20);
+    skipList.insert(30);
+    skipList.insert(40);
+
+    skipList.display();
+
+    std::cout << "Searching for 20: " << skipList.search(20) << std::endl; // Should be true
+    std::cout << "Searching for 25: " << skipList.search(25) << std::endl; // Should be false
+
+    return 0;
+}