linked-list-group-reversal-502/index.js

linked list with group reversal

const readline = require("readline");

// Node class for representing individual nodes in the linked list
class Node {
  constructor(data) {
    this.data = data;
    this.next = null;
  }
}

// LinkedList class that manages the linked list operations
class LinkedList {
  constructor() {
    this.head = null;
  }

  // Method to append a new node at the end of the list
  append(data) {
    const newNode = new Node(data);
    if (!this.head) {
      this.head = newNode;
      return;
    }

    let current = this.head;
    while (current.next) {
      current = current.next;
    }
    current.next = newNode;
  }

  // Method to reverse the linked list in groups of k
  reverseInGroups(k) {
    if (this.head === null || k <= 1) return;

    let current = this.head;
    let prevTail = null;

    while (current) {
      let count = 0;
      let groupHead = current;
      let prev = null;
      let next = null;

      // Reverse the group of 'k' nodes
      while (current && count < k) {
        next = current.next;
        current.next = prev;
        prev = current;
        current = next;
        count++;
      }

      if (!prevTail) {
        this.head = prev;
      } else {
        prevTail.next = prev;
      }

      groupHead.next = current;
      prevTail = groupHead;
    }
  }

  // Method to print the linked list
  print() {
    let current = this.head;
    let result = "";
    while (current) {
      result += current.data + " -> ";
      current = current.next;
    }
    result += "null";
    console.log(result);
  }
}

// Setup readline interface for user input
const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
});

// Function to ask user for input
function askQuestion(query) {
  return new Promise((resolve) => rl.question(query, resolve));
}

// Main function to execute the program
async function main() {
  const list = new LinkedList();

  const values = await askQuestion(
    "Enter the values for the linked list (comma separated): "
  );
  const valueArray = values.split(",").map((value) => value.trim());

  for (const value of valueArray) {
    list.append(parseInt(value));
  }

  const k = await askQuestion(
    "Enter the value of k (group size for reversal): "
  );

  console.log("Original List:");
  list.print();

  list.reverseInGroups(parseInt(k));

  console.log(`List After Reversing in Groups of ${k}:`);
  list.print();

  rl.close();
}

// Run the main function
main();