reversing_ll.cpp

#include <iostream>
#include <vector>

using namespace std;

class LLNode {
public:
  int data;
  LLNode *next;
  LLNode();
  LLNode(int);
  void printll();
  void appendtoTail(int);
  LLNode *reverseList();
};

LLNode::LLNode() : data(0), next(NULL) {}
LLNode::LLNode(int data) : data(data), next(NULL) {}

void LLNode::printll() {
  LLNode *currentNode = this;

  while (currentNode->next != NULL) {
    cout << currentNode->data << "->";
    currentNode = currentNode->next;
  }
  cout << currentNode->data << '\n';
  return;
}

void LLNode::appendtoTail(int data) {
  LLNode *currentNode = this;
  while (currentNode->next != NULL)
    currentNode = currentNode->next;
  currentNode->next = new LLNode(data);
  return;
}

LLNode *LLNode::reverseList() {

  LLNode *head = this;
  LLNode *current = this;
  LLNode *prev = NULL;
  LLNode *next = current->next;

  while (next != NULL) {
    current->next = prev;
    prev = current;
    current = next;
    next = current->next;
  }

  current->next = prev;
  head = current;

  return head;
}

LLNode *createLL(vector<int> &vals) {
  LLNode *head = new LLNode(vals[0]);
  vector<int>::iterator it;

  LLNode *currentNode = head;
  for (it = vals.begin() + 1; it != vals.end(); it++) {
    currentNode->next = new LLNode(*it);
    currentNode = currentNode->next;
  }

  return head;
}

int main([[maybe_unused]] int argc, [[maybe_unused]] char **argv) {
  vector<int> vals{1, 2, 3, 4, 5, 6, 7, 8};

  LLNode *head = createLL(vals);

  head->printll();

  head = head->reverseList();
  head->printll();
}