LRU Cache

mediumcodingAlgorithmsDesignHash MapLinked Lists~30 min

Asked at Google, Meta, Stripe

Overview

Design a data structure for a Least Recently Used (LRU) cache. It should support:

get(key) — return the value or -1 if not found
put(key, value) — insert/update and evict the least recently used key if at capacity

Both operations must be O(1).

Constraints

1 <= capacity <= 3000
0 <= key, value <= 10,000

Examples

const c = new LRUCache(2);
c.put(1, 1); c.put(2, 2);
c.get(1);    // => 1
c.put(3, 3); // evicts key 2
c.get(2);    // => -1

Solution

Reveal solution

class LRUCache {
  constructor(capacity) {
    this.cap = capacity;
    this.map = new Map();
  }
  get(key) {
    if (!this.map.has(key)) return -1;
    const val = this.map.get(key);
    this.map.delete(key);
    this.map.set(key, val);
    return val;
  }
  put(key, value) {
    this.map.delete(key);
    this.map.set(key, value);
    if (this.map.size > this.cap) {
      this.map.delete(this.map.keys().next().value);
    }
  }
}

JavaScript's Map maintains insertion order, so the first key is the LRU.

Resources

LRU Cache — LeetCode

lru-cache.js

LRU Cache

mediumcodingAlgorithmsDesign

Overview

Design a data structure for a Least Recently Used (LRU) cache. It should support:

get(key) — return the value or -1 if not found
put(key, value) — insert/update and evict the least recently used key if at capacity

Both operations must be O(1).

Constraints

1 <= capacity <= 3000
0 <= key, value <= 10,000

Examples

const c = new LRUCache(2);
c.put(1, 1); c.put(2, 2);
c.get(1);    // => 1
c.put(3, 3); // evicts key 2
c.get(2);    // => -1

Solution

Reveal solution

class LRUCache {
  constructor(capacity) {
    this.cap = capacity;
    this.map = new Map();
  }
  get(key) {
    if (!this.map.has(key)) return -1;
    const val = this.map.get(key);
    this.map.delete(key);
    this.map.set(key, val);
    return val;
  }
  put(key, value) {
    this.map.delete(key);
    this.map.set(key, value);
    if (this.map.size > this.cap) {
      this.map.delete(this.map.keys().next().value);
    }
  }
}

JavaScript's Map maintains insertion order, so the first key is the LRU.

Resources

LRU Cache — LeetCode

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