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simple LRU cache typescript implementation
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| import { strict as assert } from "assert"; | |
| type Node<V> = { parent?: Node<V>; next?: Node<V>; value: V }; | |
| class DoublyLinkedList<V> { | |
| private _head?: Node<V>; | |
| private _tail?: Node<V>; | |
| get head() { | |
| return this._head!; | |
| } | |
| get tail() { | |
| return this._tail!; | |
| } | |
| set head(node: Node<V>) { | |
| this._head = node; | |
| } | |
| set tail(node: Node<V>) { | |
| this._tail = node; | |
| } | |
| moveTohead(node: Node<V>) { | |
| if (this._head) this._head.parent = node; | |
| node.next = this._head; | |
| if (this._tail === node) this._tail = this._tail.parent; | |
| this._head = node; | |
| return node; | |
| } | |
| unshift(value: V) { | |
| let node = { value } as Node<V>; | |
| let _head = this._head; | |
| this._head = node; | |
| this._head.next = _head; | |
| if (_head) _head.parent = node; | |
| if (!this._tail) this._tail = node; | |
| return node; | |
| } | |
| pop() { | |
| const _tail = this._tail!; | |
| this._tail = _tail.parent; | |
| return _tail; | |
| } | |
| index(n: number) { | |
| let count = 0; | |
| let node: Node<V> | undefined = this._head; | |
| while (node && count < n) { | |
| node = node.next as Node<V>; | |
| count++; | |
| } | |
| return node; | |
| } | |
| } | |
| class LRU<K, V> { | |
| private _size = 0; | |
| private cache = new Map<K, Node<V>>(); | |
| private weakKeyMap = new WeakMap<Node<V>, K>(); | |
| private _dll = new DoublyLinkedList<V>(); | |
| constructor(private max: number) {} | |
| get size() { | |
| return this._size; | |
| } | |
| get dll() { | |
| return this._dll; | |
| } | |
| get(key: K): Node<V> | undefined { | |
| if (this.cache.has(key)) { | |
| const node = this.cache.get(key); | |
| return this._dll.moveTohead(node!); | |
| } | |
| } | |
| set(key: K, value: V) { | |
| if (this.cache.has(key)) { | |
| let node = this.cache.get(key)!; | |
| node.value = value; | |
| return this._dll.moveTohead(node); | |
| } | |
| let node = this._dll.unshift(value); | |
| this.weakKeyMap.set(node, key); | |
| this.cache.set(key, node); | |
| this._size++; | |
| if (this._size > this.max) { | |
| this.cache.delete(this.weakKeyMap.get(this._dll.pop())!); | |
| this._size--; | |
| } | |
| return node; | |
| } | |
| } | |
| const lru = new LRU<string, number>(3); | |
| lru.set("one", 1); | |
| assert.equal(lru.dll.index(0)!.value, 1, "index(0) value should equal 1"); | |
| assert.equal( | |
| lru.dll.head.value, | |
| 1, | |
| "head value should equal 1, the same as index(0)" | |
| ); | |
| lru.set("two", 2); | |
| assert.equal(lru.dll.index(0)!.value, 2); | |
| assert.equal( | |
| lru.dll.head.value, | |
| 2, | |
| "head value should equal 2, the same as index(0)" | |
| ); | |
| lru.set("three", 3); | |
| assert.equal(lru.dll.index(0)!.value, 3); | |
| assert.equal(lru.dll.tail!.value, 1, "tail value should equal 1"); | |
| lru.set("three", 333); | |
| assert.equal( | |
| lru.dll.index(0)!.value, | |
| 333, | |
| "should replace value of existing key" | |
| ); | |
| assert.equal(lru.size, 3, "lru size should remain at 3"); | |
| assert.equal(lru.dll.head!.value, 333, "head value should equal 333"); | |
| assert.equal(lru.dll.tail!.value, 1, "tail value should equal 1"); | |
| lru.set("four", 4); | |
| assert.equal(lru.dll.tail!.value, 2, "new tail value should equal 2"); |
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