Create MergeSort_linkedlist.cpp

array/MergeSort_linkedlist.cpp

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+#include<iostream>
+using namespace std;
+
+//Node structure
+struct Node{
+	int data;
+	Node *next;
+};
+
+//function to insert in list
+void insert(int x,Node **head) {
+	if(*head == NULL){
+		*head = new Node;
+		(*head)->data = x;
+		(*head)->next = NULL;
+		return;
+	}
+	Node *temp = new Node;
+	temp->data = (*head)->data;
+	temp->next = (*head)->next;
+	(*head)->data=x;
+	(*head)->next=temp;
+}
+
+//function to print the list
+void print(Node *head) {
+	Node *temp=head;
+	while(temp!=NULL) {
+		cout<<temp->data<<" ";
+		temp = temp->next;
+	}
+}
+
+Node *merge(Node *firstNode,Node *secondNode) {
+	Node *merged = new Node;
+	Node *temp = new Node;
+
+	//merged is equal to temp so in the end we have the top Node.
+	merged = temp;
+
+	//while either firstNode or secondNode becomes NULL
+	while(firstNode != NULL && secondNode != NULL) {
+
+		if(firstNode->data<=secondNode->data) {
+			temp->next = firstNode;
+			firstNode = firstNode->next;
+		}
+
+		else {
+			temp->next = secondNode;
+			secondNode = secondNode->next;
+		}
+		temp = temp->next;
+	}
+
+//any remaining Node in firstNode or secondNode gets inserted in the temp List
+	while(firstNode!=NULL) {
+		temp->next = firstNode;
+		firstNode = firstNode->next;
+		temp = temp->next;
+	}
+
+	while(secondNode!=NULL) {
+		temp->next = secondNode;
+		secondNode = secondNode->next;
+		temp = temp->next;
+	}
+	//return the head of the sorted list
+	return merged->next;
+}
+
+//function to calculate the middle Element
+Node *middle(Node *head) {
+	Node *slow = head;
+	Node *fast = head->next;
+
+	while(slow->next != NULL && (fast!=NULL && fast->next!=NULL)) {
+		slow = slow->next;
+		fast = fast->next->next;
+	}
+	return slow;
+}
+
+//function to sort the given list
+Node *sort(Node *head){
+
+	if(head->next == NULL) {
+		return head;
+	}
+
+	Node *mid = new Node;
+	Node *head2 = new Node;
+	mid = middle(head);
+	head2 = mid->next;
+	mid->next = NULL;
+	//recursive call to sort() hence diving our problem, and then merging the solution
+	Node *finalhead = merge(sort(head),sort(head2));
+	return finalhead;
+}
+int main(void) {
+	Node *head = NULL;
+	int n[]={7,10,5,20,3,2};
+	for(int i=0;i<6;i++) {
+		insert(n[i],&head); //inserting in the list
+	}
+cout<<"\nSorted Linked List is: \n";
+	print(sort(head));	 //printing the sorted list returned by sort()
+	return 0;
+}