Merge pull request #177 from kiruba-r11/feature-1

Added Recursive Reverse in Circular Linked Lists

Author: smv1999

Data Structures/Linked Lists/Circular Linked Lists/recursive_reverse.cpp

@@ -0,0 +1,127 @@
+/*
+
+This is a Circular Linked List program which reverses the Linked List recursively.
+
+Since, it is a Circular Linked List, the last node would point to the head node.
+
+*/
+
+#include <iostream>
+
+using namespace std;
+
+/*
+
+Node definition:
+	1. Integer Data
+	2. Pointer to next node.
+
+*/
+
+class cll_node {
+public: 
+	int data;
+	cll_node* next;
+};
+
+void createCLL(cll_node* &head) {
+
+	int choice;
+
+	cll_node* temp = head;
+
+	do {
+		int data;
+
+		cout << "Enter Data : ";
+		cin >> data;
+
+		cll_node* newNode = new cll_node();
+		newNode->data = data;
+		newNode->next = NULL;
+
+		if(head == NULL) {
+			head = newNode;
+			newNode->next = head;
+			temp = head;
+		} else {
+			temp->next = newNode;
+			temp = newNode;
+			temp->next = head;
+		}
+
+		cout << "Do you want to continue? (1/0) : ";
+		cin >> choice;
+
+	} while(choice == 1);
+
+}
+
+cll_node* recursive_reverse_helper(cll_node* head , cll_node* tail) {
+
+	if(head == NULL || head->next == head)
+		return head;
+
+	// O(1)
+	/*
+		// O(n)
+		// cll_node* tail = head;
+		// while(tail->next != head) {
+		// 	tail = tail->next;
+		// }
+	*/
+
+	tail->next = head->next;
+	cll_node* temp = head->next;
+
+	cll_node* newHead = recursive_reverse_helper(temp , tail);
+
+	temp->next = head;
+	head->next = newHead;
+	return newHead;
+
+}
+
+cll_node* recursive_reverse(cll_node* head) {
+
+	if(head == NULL || head->next == head)
+		return head;
+
+	cll_node* tail = head;
+
+	while(tail->next != head) {
+		tail = tail->next;
+	}
+
+	return recursive_reverse_helper(head , tail);
+}
+
+void display(cll_node* head) {
+	cout << "The elements are : ";
+	if(head == NULL)
+		return;
+	cll_node* temp = head;
+
+	do {
+		cout << temp->data << " ";
+		temp = temp->next;
+	} while(temp != head);
+	cout << endl;
+}
+
+int main() {
+
+	cll_node* head = NULL;
+
+	createCLL(head);
+
+	cout << "Before reversing : " << endl;
+	display(head);
+
+	head = recursive_reverse(head);
+
+	cout << "After reversing : " << endl;
+	display(head);
+
+	return 0;
+}