Update b_e

src/lib/lru-cache.ts

@@ -0,0 +1,139 @@
+/**
+* A LRU cache intended for caching pure functions.
+*/
+export class LRUCache<K, V> {
+    private map = new Map<K, ListNode<K, V>>();
+    // Invariant: Exactly one of the below is true before and after calling a
+    // LRUCache method:
+    // - first and last are both undefined, and map.size() is 0.
+    // - first and last are the same object, and map.size() is 1.
+    // - first and last are different objects, and map.size() is greater than 1.
+    private first: ListNode<K, V> | undefined = undefined;
+    private last: ListNode<K, V> | undefined = undefined;
+    maxSize: number;
+    
+    /**
+    * @param maxSize The maximum size for this cache. We recommend setting this
+    * to be one less than a power of 2, as most hashtables - including V8's
+    * Object hashtable (https://crsrc.org/c/v8/src/objects/ordered-hash-table.cc)
+    * - uses powers of two for hashtable sizes. It can't exactly be a power of
+    * two, as a .set() call could temporarily set the size of the map to be
+    * maxSize + 1.
+    */
+    constructor(maxSize: number) {
+        this.maxSize = maxSize;
+    }
+    
+    get size(): number {
+        return this.map.size;
+    }
+    
+    /**
+    * Gets the specified key from the cache, or undefined if it is not in the
+    * cache.
+    * @param key The key to get.
+    * @returns The cached value, or undefined if key is not in the cache.
+    */
+    get(key: K): V | undefined {
+        const node = this.map.get(key);
+        if (node === undefined) {
+            return undefined;
+        }
+        // It is guaranteed that there is at least one item in the cache.
+        // Therefore, first and last are guaranteed to be a ListNode...
+        // but if there is only one item, they might be the same.
+        
+        // Update the order of the list to make this node the first node in the
+        // list.
+        // This isn't needed if this node is already the first node in the list.
+        if (node !== this.first) {
+            // As this node is DIFFERENT from the first node, it is guaranteed that
+            // there are at least two items in the cache.
+            // However, this node could possibly be the last item.
+            if (node === this.last) {
+                // This node IS the last node.
+                this.last = node.prev;
+                // From the invariants, there must be at least two items in the cache,
+                // so node - which is the original "last node" - must have a defined
+                // previous node. Therefore, this.last - set above - must be defined
+                // here.
+                // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+                this.last!.next = undefined;
+            } else {
+                // This node is somewhere in the middle of the list, so there must be at
+                // least THREE items in the list, and this node's prev and next must be
+                // defined here.
+                // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+                node.prev!.next = node.next;
+                // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+                node.next!.prev = node.prev;
+            }
+            node.next = this.first;
+            // From the invariants, there must be at least two items in the cache, so
+            // this.first must be a valid ListNode.
+            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+            this.first!.prev = node;
+            this.first = node;
+        }
+        return node.value;
+    }
+    
+    /**
+    * Sets an entry in the cache.
+    *
+    * @param key The key of the entry.
+    * @param value The value of the entry.
+    * @throws Error, if the map already contains the key.
+    */
+    set(key: K, value: V): void {
+        // Ensure that this.maxSize >= 1.
+        if (this.maxSize < 1) {
+            return;
+        }
+        if (this.map.has(key)) {
+            throw new Error("Cannot update existing keys in the cache");
+        }
+        const node = new ListNode(key, value);
+        // Move node to the front of the list.
+        if (this.first === undefined) {
+            // If the first is undefined, the last is undefined too.
+            // Therefore, this cache has no items in it.
+            this.first = node;
+            this.last = node;
+        } else {
+            // This cache has at least one item in it.
+            node.next = this.first;
+            this.first.prev = node;
+            this.first = node;
+        }
+        this.map.set(key, node);
+        
+        while (this.map.size > this.maxSize) {
+            // We are guaranteed that this.maxSize >= 1,
+            // so this.map.size is guaranteed to be >= 2,
+            // so this.first and this.last must be different valid ListNodes,
+            // and this.last.prev must also be a valid ListNode (possibly this.first).
+            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+            const last = this.last!;
+            this.map.delete(last.key);
+            this.last = last.prev;
+            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+            this.last!.next = undefined;
+        }
+    }
+}
+
+/**
+* A node in a doubly linked list.
+*/
+class ListNode<K, V> {
+    key: K;
+    value: V;
+    next: ListNode<K, V> | undefined = undefined;
+    prev: ListNode<K, V> | undefined = undefined;
+    
+    constructor(key: K, value: V) {
+        this.key = key;
+        this.value = value;
+    }
+}