Added the k-grouped reverse a linked list algorithm.

Author: swainsubrat

Linked List/reverse_k-group_linkedList.cpp

@@ -0,0 +1,98 @@
+// CPP program to reverse a linked list 
+// in groups of given size  
+#include <bits/stdc++.h> 
+using namespace std; 
+  
+/* Link list node */
+class Node  
+{  
+    public: 
+    int data;  
+    Node* next;  
+};  
+  
+/* Reverses the linked list in groups 
+of size k and returns the pointer 
+to the new head node. */
+Node *reverse (Node *head, int k)  
+{  
+    Node* current = head;  
+    Node* next = NULL;  
+    Node* prev = NULL;  
+    int count = 0;  
+      
+    /*reverse first k nodes of the linked list */
+    while (current != NULL && count < k)  
+    {  
+        next = current->next;  
+        current->next = prev;  
+        prev = current;  
+        current = next;  
+        count++;  
+    }  
+      
+    /* next is now a pointer to (k+1)th node  
+    Recursively call for the list starting from current.  
+    And make rest of the list as next of first node */
+    if (next != NULL)  
+    head->next = reverse(next, k);  
+  
+    /* prev is new head of the input list */
+    return prev;  
+}  
+  
+/* UTILITY FUNCTIONS */
+/* Function to push a node */
+void push(Node** head_ref, int new_data)  
+{  
+    /* allocate node */
+    Node* new_node = new Node(); 
+  
+    /* put in the data */
+    new_node->data = new_data;  
+  
+    /* link the old list off the new node */
+    new_node->next = (*head_ref);      
+  
+    /* move the head to point to the new node */
+    (*head_ref) = new_node;  
+}  
+  
+/* Function to print linked list */
+void printList(Node *node)  
+{  
+    while (node != NULL)  
+    {  
+        cout<<node->data<<" ";  
+        node = node->next;  
+    }  
+}  
+  
+/* Driver code*/
+int main()  
+{  
+    /* Start with the empty list */
+    Node* head = NULL;  
+  
+    /* Created Linked list is 1->2->3->4->5->6->7->8->9 */
+    push(&head, 9);  
+    push(&head, 8);  
+    push(&head, 7);  
+    push(&head, 6);  
+    push(&head, 5);  
+    push(&head, 4);  
+    push(&head, 3);  
+    push(&head, 2);  
+    push(&head, 1);      
+  
+    cout<<"Given linked list \n";  
+    printList(head);  
+    head = reverse(head, 3);  
+  
+    cout<<"\nReversed Linked list \n";  
+    printList(head);  
+  
+    return(0);  
+}  
+  
+// This code is contributed by Subrat Kumar Swain