Day 24 reverse linkedlist iterative,recursive

linked_list_problems/reverseLinkedListIterAndRecurse.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+
+struct Node {
+  int data;
+  Node * next;
+  Node( int d ) : data{ d }, next{ nullptr } { }
+};
+
+void push( Node * & head, int data ) {
+  Node *newNode = new Node(data);
+  if ( head == nullptr ) {
+    head = newNode;
+  } else {
+    Node *curr = head;
+    while( curr->next != nullptr ) {
+      curr = curr->next;
+    }
+    curr->next = newNode;
+  }
+}
+
+void printList( Node * head ) {
+  while( head ) {
+    std::cout << head->data << "-->";
+    head = head->next;
+  }
+  std::cout << "NULL" << std::endl;
+}
+
+void reverseIter( Node * & head ) {
+  //length of list is less than 2
+  if ( head == nullptr || ( head != nullptr && head->next == nullptr )) {
+    return;
+  }
+  Node *newHead = nullptr;
+  Node *curr = head;
+  Node *prev = nullptr;
+  while( curr != nullptr ) {
+    prev = curr;
+    curr = curr->next;
+    prev->next = newHead;
+    newHead = prev;
+  }
+  head = newHead;
+}
+
+void reverseRecur( Node * & head ) {
+  if ( head == nullptr || ( head != nullptr && head->next == nullptr ) ) {
+    return;
+  }
+  Node * first = head;
+  Node * rest = head->next;
+  reverseIter( rest );
+  first->next->next = first;
+  first->next = nullptr;
+  head = rest;
+}
+
+int main() {
+  Node *head = nullptr;
+  push( head, 1 );
+  push( head, 2 );
+  push( head, 3 );
+  push( head, 4 );
+  push( head, 5 );
+  std::cout << "Before Reversing Linkedlist:      ";
+  printList( head );
+  reverseIter( head );
+  std::cout << "After Reversing Linkedlist once:  ";
+  printList( head );
+  reverseRecur( head );
+  std::cout << "After Reversing Linkedlist twice: ";
+  printList( head );
+  return 0;
+}