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Added CycleNode Algorithm #754

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1 change: 1 addition & 0 deletions DIRECTORY.md
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,7 @@
* [MinPriorityQueue](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Heap/MinPriorityQueue.js)
* Linked-List
* [CycleDetection](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Linked-List/CycleDetection.js)
* [CycleNode](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Linked-List/CycleNode.js)
* [DoublyLinkedList](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Linked-List/DoublyLinkedList.js)
* [RotateListRight](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Linked-List/RotateListRight.js)
* [SingleCircularLinkedList](https://github.com/TheAlgorithms/Javascript/blob/master/Data-Structures/Linked-List/SingleCircularLinkedList.js.js)
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42 changes: 42 additions & 0 deletions Data-Structures/Linked-List/CycleNode.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
/*
Problem: Given a linked list, return the node where cycle begins. If there is no cycle return null

Approach used: Floyd Cycle Detection Algorithm

What is Floyd Cycle Detection Algorithm?
- Floyd Cyclce Detection algorithm uses two pointer (slow & fast), in which fast pointer move twice the speed of slow pointer.
- It is also known as hare and tortoise algorithm as we can imagine slow pointer as tortoise that moves slow and hare as the fast one.
- If the fast pointer reaches null, that means there was no cycle.
- If the fast pointer and slow pointer becomes equal that means there was cycle.

For reference: https://www.codingninjas.com/blog/2020/09/09/floyds-cycle-detection-algorithm/
*/

/*
Input: Pass the head (first node) of linked list
*/
const detectCycleNode = (head) => {
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@raklaptudirm raklaptudirm Oct 8, 2021

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Add a specification for head. What type of input do you expect?

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@raklaptudirm raklaptudirm Oct 8, 2021

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That is not what I meant. I mean what properties and function do you expect the head parameter to implement. Write a specification for the head parameter.

if (!head || !head.next) {
return null
}

let slow = head
let fast = head

while (fast && fast.next) {
slow = slow.next
fast = fast.next.next
if (slow === fast) break
}

slow = head

while (fast && slow !== fast) {
slow = slow.next
fast = fast.next
}

return fast
}

export { detectCycleNode }

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