reverse linked list

C++/reverseLinkedList.cpp

@@ -0,0 +1,114 @@
+#include <bits/stdc++.h>
+using namespace std;
+class node
+{
+public:
+ int data;
+ node *next;
+ node(int val)
+ {
+ data = val;
+ next = NULL;
+ }
+};
+// iterative approach
+node *reverse(node *&head)
+{
+ node *prevPtr = NULL;
+ node *currPtr = head;
+ node *nextPtr;
+ while (currPtr != NULL)
+ {
+ nextPtr = currPtr->next;
+ currPtr->next = prevPtr;
+ prevPtr = currPtr;
+ currPtr = nextPtr;
+ }
+ return prevPtr; // new head
+}
+
+// recursive approach
+node *reverseRecursive(node *&head)
+{
+
+ // base condition
+ if (head == NULL || head->next == NULL)
+ {
+ return head;
+ }
+ node *newHead = reverseRecursive(head->next);
+ head->next->next = head;
+ head->next = NULL;
+ return newHead;
+}
+
+node *reverseK(node *&head, int k)
+{
+ node *prevPtr = NULL;
+ node *currPtr = head;
+ node *nextPtr;
+ int count = 0;
+ while (currPtr != NULL && count < k)
+ {
+ nextPtr = currPtr->next;
+ currPtr->next = prevPtr;
+ prevPtr = currPtr;
+ currPtr = nextPtr;
+
+ count++;
+ } // k nodes
+
+ if (nextPtr != NULL)
+ {
+ head->next = reverseK(nextPtr, k);
+ }
+ return prevPtr;
+}
+void insertAtTail(node *&head, int val)
+{
+
+ node *newNode = new node(val); // created a new node;
+ if (head == NULL)
+ {
+ head = newNode;
+ return;
+ // here you can simply call insertAtBeginning
+ }
+ node *temp = head;
+ while (temp->next != NULL)
+ {
+ temp = temp->next;
+ }
+ temp->next = newNode;
+ // as our new node already points to NULL in its next so we simply do nothing
+}
+
+void display(node *head)
+{
+
+ if (head == NULL)
+ {
+ cout << "NULL" << endl;
+ return;
+ }
+ node *temp = head;
+ while (temp != NULL)
+ {
+ cout << temp->data << "->";
+ temp = temp->next;
+ }
+ cout << "NULL" << endl;
+}
+
+int main()
+{
+ node *head = NULL;
+ insertAtTail(head, 1);
+ insertAtTail(head, 23);
+ insertAtTail(head, 12);
+ insertAtTail(head, 10);
+ display(head);
+ int k = 2;
+ node *newHead = reverseK(head, k);
+ display(newHead);
+}