Merge pull request #366 from amanvatss/master

Merge Sort Implementation Using Linked Lists #357

Algorithms/Sorting Algorithms/cpp/linkedlist/mergesort.cpp

@@ -0,0 +1,162 @@
+// In this code script we have done "sorting of linked list using mergesort" this is the important concept of the Data Strcture and Algorithm
+#include<iostream>
+using namespace std;
+
+/*
+    We created a class named as node 
+    In which put data and its next
+    and made a constructor.
+*/
+
+class node {                     
+    public:
+    int data;
+    node* next;
+
+    node(int data) {
+        this->data = data;
+        this->next = NULL;
+    }
+};
+
+// Function to insert a node at the end of the linked list
+void insertAtTail(node* &head, int data) {
+    node* newNode = new node(data);
+    if (head == NULL) {
+        head = newNode;
+        return;
+    }
+    node* temp = head;
+    while (temp->next != NULL) {
+        temp = temp->next;
+    }
+    temp->next = newNode;
+}
+
+// Function to print the linked list
+void printList(node* head) {
+    node* temp = head;
+    while (temp != NULL) {
+        cout << temp->data << " -> ";
+        temp = temp->next;
+    }
+    cout << "NULL" << endl;
+}
+
+// Function to find the middle of the linked list
+node* findmid(node* head) {
+    node* slow = head;
+    node* fast = head->next;
+
+    while (fast != NULL && fast->next != NULL) {
+        slow = slow->next;
+        fast = fast->next->next;
+    }
+    return slow;
+}
+
+// Function to merge two sorted linked lists
+node* merge(node* left, node* right) {
+    if (left == NULL)
+        return right;
+
+    if (right == NULL)
+        return left;
+
+    node* ans = new node(-1);
+    node* temp = ans;
+
+    while (left != NULL && right != NULL) {
+        if (left->data < right->data) {
+            temp->next = left;
+            temp = left;
+            left = left->next;
+        } else {
+            temp->next = right;
+            temp = right;
+            right = right->next;
+        }
+    }
+
+    while (left != NULL) {
+        temp->next = left;
+        temp = left;
+        left = left->next;
+    }
+
+    while (right != NULL) {
+        temp->next = right;
+        temp = right;
+        right = right->next;
+    }
+
+    ans = ans->next;
+    return ans;
+}
+
+// Function to perform merge sort on a linked list
+node* MergeSort(node* head) {
+    if (head == NULL || head->next == NULL) {
+        return head;
+    }
+
+    node* mid = findmid(head);
+
+    node* left = head;
+    node* right = mid->next;
+    mid->next = NULL;
+
+    left = MergeSort(left);
+    right = MergeSort(right);
+
+    node* result = merge(left, right);
+    return result;
+}
+
+int main() {
+    node* head = NULL;
+    int choice;
+    int data, n;
+                                                                        // used switch case to ask user what to do
+    do {
+        cout << "\nMenu:\n";
+        cout << "1. Insert elements into linked list\n";
+        cout << "2. Sort the linked list using Merge Sort\n";
+        cout << "3. Display the linked list\n";
+        cout << "4. Exit\n";
+        cout << "Enter your choice: ";
+        cin >> choice;
+
+        switch (choice) {
+            case 1:
+                cout << "How many values would you like to insert? ";
+                cin >> n;
+                cout << "Enter " << n << " values: ";
+                for (int i = 0; i < n; i++) {
+                    cin >> data;
+                    insertAtTail(head, data);
+                }
+                break;
+
+            case 2:
+                head = MergeSort(head);
+                cout << "Linked list sorted using Merge Sort.\n";
+                break;
+
+            case 3:
+                cout << "Current Linked List: ";
+                printList(head);
+                break;
+
+            case 4:
+                cout << "Exiting...\n";
+                break;
+
+            default:
+                cout << "Invalid choice! Please try again.\n";
+                break;
+        }
+    } while (choice != 4);
+
+    return 0;
+}