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| 1 | +class LRUCache { |
| 2 | + constructor(capacity) { |
| 3 | + this.capacity = capacity; |
| 4 | + this.cache = {}; |
| 5 | + this.head = null; |
| 6 | + this.tail = null; |
| 7 | + } |
| 8 | + |
| 9 | + get(key) { |
| 10 | + if (this.cache[key]) { |
| 11 | + this.moveToFront(key); |
| 12 | + return this.cache[key].value; |
| 13 | + } |
| 14 | + return null; |
| 15 | + } |
| 16 | + |
| 17 | + put(key, value) { |
| 18 | + if (this.cache[key]) { |
| 19 | + this.cache[key].value = value; |
| 20 | + this.moveToFront(key); |
| 21 | + } else { |
| 22 | + if (Object.keys(this.cache).length === this.capacity) { |
| 23 | + this.removeLast(); |
| 24 | + } |
| 25 | + this.addToFront(key, value); |
| 26 | + } |
| 27 | + } |
| 28 | + |
| 29 | + addToFront(key, value) { |
| 30 | + const newNode = {key, value, next: null}; |
| 31 | + if (!this.head) { |
| 32 | + this.head = newNode; |
| 33 | + this.tail = newNode; |
| 34 | + } else { |
| 35 | + newNode.next = this.head; |
| 36 | + this.head = newNode; |
| 37 | + } |
| 38 | + this.cache[key] = newNode; |
| 39 | + } |
| 40 | + |
| 41 | + removeLast() { |
| 42 | + if (!this.head) return; |
| 43 | + |
| 44 | + const lastKey = this.tail.key; |
| 45 | + delete this.cache[lastKey]; |
| 46 | + |
| 47 | + if (this.head === this.tail) { |
| 48 | + this.head = null; |
| 49 | + this.tail = null; |
| 50 | + } else { |
| 51 | + let current = this.head; |
| 52 | + while (current.next !== this.tail) { |
| 53 | + current = current.next; |
| 54 | + } |
| 55 | + |
| 56 | + current.next = null; |
| 57 | + this.tail = current; |
| 58 | + } |
| 59 | + } |
| 60 | + |
| 61 | + moveToFront(key) { |
| 62 | + const current = this.cache[key]; |
| 63 | + |
| 64 | + if (current === this.head) return; |
| 65 | + |
| 66 | + let prev = null; |
| 67 | + let node = this.head; |
| 68 | + while (node && node.key !== key) { |
| 69 | + prev = node; |
| 70 | + node = node.next; |
| 71 | + } |
| 72 | + |
| 73 | + if (!node) return; |
| 74 | + |
| 75 | + if (node === this.tail) { |
| 76 | + this.tail = prev; |
| 77 | + } |
| 78 | + |
| 79 | + if (prev) { |
| 80 | + prev.next = node.next; |
| 81 | + } |
| 82 | + |
| 83 | + node.next = this.head; |
| 84 | + this.head = node; |
| 85 | + } |
| 86 | +} |
| 87 | + |
| 88 | +// Custom Hook in React JS 👇 |
| 89 | +import {useRef} from "react"; |
| 90 | + |
| 91 | +const useLRUCache = (capacity) => { |
| 92 | + const cacheRef = useRef(new LRUCache(capacity)); |
| 93 | + console.log(cacheRef.current); |
| 94 | + |
| 95 | + const get = (key) => cacheRef.current.get(key); |
| 96 | + const put = (key, value) => cacheRef.current.put(key, value); |
| 97 | + |
| 98 | + return {get, put}; |
| 99 | +}; |
| 100 | + |
| 101 | +export default useLRUCache; |
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