educative.io

A More readable solution

Courses
,
#1 
class Node {
  constructor(value, next = null) {
    this.value = value;
    this.next = next;
  }

  get_list() {
    result = "";
    temp = this;
    while (temp !== null) {
      result += temp.value + " ";
      temp = temp.next;
    }
    return result;
  }
};



const reverse_every_k_elements = function (head, k) {
  let curr = head
  let prev = null

  while (true) {
    let i = 0
    // after reversing, this ref to curr will be the last node of the section
    const lastNodeOfCurrRevSection = curr  
    const lastNodeOfLastRevSection = prev
      

    // reverse k nodes
    while (curr !== null && i < k) {
      const next = curr.next
      curr.next = prev
      prev = curr
      curr = next
      i += 1
    }

    const firstNodeOfCurrentRevSection = prev

    if (lastNodeOfLastRevSection === null) {
      // start of the list, set new head
      head = firstNodeOfCurrentRevSection
    } else {
      // link the last reversed list with the one we just reversed
      lastNodeOfLastRevSection.next = firstNodeOfCurrentRevSection
    }    

    // link the current reversed list with the next unreversed section
    lastNodeOfCurrRevSection.next = curr

    // break if we reached the end of the list
    if (curr === null) {
      break
    }

    // pass the last node of the list we just reversed 
    // to the next iteration
    prev = lastNodeOfCurrRevSection
  }

  return head
}


head = new Node(1)
head.next = new Node(2)
head.next.next = new Node(3)
head.next.next.next = new Node(4)
head.next.next.next.next = new Node(5)
head.next.next.next.next.next = new Node(6)
head.next.next.next.next.next.next = new Node(7)
head.next.next.next.next.next.next.next = new Node(8)

console.log(`Nodes of original LinkedList are: ${head.get_list()}`)
console.log(`Nodes of reversed LinkedList are: ${reverse_every_k_elements(head, 3).get_list()}`)

Course: Grokking the Coding Interview: Patterns for Coding Questions - Learn Interactively
Lesson: Reverse every K-element Sub-list (medium) - Grokking the Coding Interview: Patterns for Coding Questions

Course: Grokking the Coding Interview: Patterns for Coding Questions - Learn Interactively
Lesson: Reverse every K-element Sub-list (medium) - Grokking the Coding Interview: Patterns for Coding Questions

Course: Grokking the Coding Interview: Patterns for Coding Questions - Learn Interactively
Lesson: Reverse every K-element Sub-list (medium) - Grokking the Coding Interview: Patterns for Coding Questions

1 Like
#2

Hello @Nicolas_F ,

Thanks for sharing the code. It is the same as the solution discussed in this lesson, you have missed the part where k <1.
Please include the following code in your code.
if (k <= 1 || head === null) {
return head;
}