LRU Cache - Least Recently Used

class LRUCache {
    constructor(capacity) {
        this.capacity = capacity;
        this.cache = new Map();
    }

    get(key) {
        if (!this.cache.has(key)) return -1;

        // Move to end (most recently used)
        const value = this.cache.get(key);
        this.cache.delete(key);
        this.cache.set(key, value);
        return value;
    }

    put(key, value) {
        if (this.cache.has(key)) {
            // Update existing
            this.cache.delete(key);
        } else if (this.cache.size >= this.capacity) {
            // Remove least recently used (first item)
            const firstKey = this.cache.keys().next().value;
            this.cache.delete(firstKey);
        }

        this.cache.set(key, value);
    }

    // Advanced: With TTL (Time To Live)
    setWithTTL(key, value, ttl) {
        this.put(key, {
            value,
            expiresAt: Date.now() + ttl
        });
    }

    getWithTTL(key) {
        const item = this.get(key);
        if (item === -1) return -1;

        if (item.expiresAt && Date.now() > item.expiresAt) {
            this.cache.delete(key);
            return -1;
        }

        return item.value || item;
    }
}

// Usage
const cache = new LRUCache(3);
cache.put(1, 'a');
cache.put(2, 'b');
cache.put(3, 'c');
cache.get(1); // Moves 1 to end
cache.put(4, 'd'); // Removes 2 (LRU)