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doubly link list #32

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ashokdey merged 8 commits into master from DoublyLinkList
Oct 8, 2019
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7 changes: 6 additions & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -34,9 +34,9 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
- [Queue](src/_DataStructures_/Queue)
- [Weave](src/_DataStructures_/Queue/weave)

- [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
- [Suffix Tree](src/_DataStructures_/SuffixTree)


### Logical Problems

- [Anagrams](src/_Problems_/anagrams)
Expand All @@ -63,6 +63,11 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct

- [Binary Search](src/_Searching_/BinarySearch)

### Algorithms

- [LRU Cache](src/_Algorithms_/lru-cache)


### Path Finder

- [A\*](src/PathFinder/AStart)
Expand Down
71 changes: 71 additions & 0 deletions src/_Algorithms_/lru-cache/index.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,71 @@
/*
Least recently used (LRU) - cache implementation

get(key) – Get the value (will always be positive) of the key if the key exists in the cache, otherwise return false.
Complexity: O(1)

set(key, value) – Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.
Complexity: O(1)
*/

const DoublyLinkedList = require('../../_DataStructures_/DoublyLinkedList/index');

class LRUCache {
constructor(n) {
this.size = n;
this.map = new Map();
this.list = new DoublyLinkedList();
}

// this method will work in O(1)
set(key, value) {
const data = {
key,
value,
};
if (!this.map.has(key)) {
this.list.addAtBeginning(data);
this.map.set(key, this.list.head.next);

if (this.list.length() > this.size) {
const lastNode = this.list.tail.previous.data;
this.map.delete(lastNode.key);
this.list.removeAtEnd();
}
} else {
this.list.remove(this.map.get(key));
this.list.addAtBeginning(data);
this.map.set(key, this.list.head.next);
}
}

// this method will work in O(1)
get(key) {
if (this.map.has(key)) {
const node = this.map.get(key);
const { value } = node.data;
this.list.remove(node);
this.list.addAtBeginning({
key,
value,
});
this.map.set(key, this.list.head.next);
}
return false;
}
}

// const lru = new LRUCache(3);
// lru.set(1, 1);
// lru.set(2, 2);
// lru.set(3, 3);
// lru.set(4, 4);
// lru.set(5, 5);
// lru.set(2, 2);
// lru.get(5, 5);
// lru.list.display();


module.exports = {
LRUCache,
};
65 changes: 65 additions & 0 deletions src/_DataStructures_/DoublyLinkedList/index.js
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@@ -0,0 +1,65 @@
/* eslint-disable class-methods-use-this */
class Node {
constructor(data, previous, next) {
this.data = data;
this.previous = previous;
this.next = next;
}
}

class DoublyLinkedList {
constructor() {
// head -> tail
// head <- tail
this.head = new Node(null, null, null);
this.tail = new Node(null, null, null);
this.head.next = this.tail; // head next point to tail
this.tail.previous = this.head; // tail previous point to head
this.size = 0;
}

addAtBeginning(value) {
const newNode = new Node(value, this.head, this.head.next);
this.head.next.previous = newNode;
this.head.next = newNode;
this.size += 1;
}

addAtEnd(value) {
const newNode = new Node(value, this.tail.previous, this.tail);
this.tail.previous.next = newNode;
this.tail.previous = newNode;
this.size += 1;
}

removeAtBeginning() {
this.remove(this.head.next);
this.size -= 1;
}

removeAtEnd() {
this.remove(this.tail.previous);
this.size -= 1;
}

remove(node) {
const previousNode = node.previous;
const nextNode = node.next;
previousNode.next = nextNode;
nextNode.previous = previousNode;
}

length() {
return this.size;
}

display() {
let address = this.head.next;
while (address !== this.tail) {
console.log(address.data);
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@ashokdey ashokdey Oct 5, 2019

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no-console

Also, make sure the code adheres to ESLint rules.

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It's a display function to print data in a linked list.

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@ashokdey ashokdey Oct 7, 2019

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Add the comment to ignore the ESLint rule

address = address.next;
}
}
}

module.exports = DoublyLinkedList;

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