Memoize II

mediumcodingJavaScriptFunctionsCaching~25 min

Asked at Meta, Google, Stripe

Overview

Implement memoize(fn) that caches results across any number of arguments. Must distinguish different argument combinations correctly.

Constraints

Support any number of arguments
Correctly distinguish [1, 2] from [1] and [2]
Use a trie-like cache structure or composite keys

Examples

const add = memoize((a, b) => a + b);
add(1, 2); // 3 (computed)
add(1, 2); // 3 (cached)
add(2, 1); // 3 (computed — different args)

Solution

Reveal solution

function memoize(fn) {
  const cache = new Map();
  return function(...args) {
    let node = cache;
    for (const arg of args) {
      if (!node.has(arg)) node.set(arg, new Map());
      node = node.get(arg);
    }
    if (node.has('__result__')) return node.get('__result__');
    const result = fn(...args);
    node.set('__result__', result);
    return result;
  };
}

memoize-ii.js

Memoize II

mediumcodingJavaScriptFunctions

Overview

Implement memoize(fn) that caches results across any number of arguments. Must distinguish different argument combinations correctly.

Constraints

Support any number of arguments
Correctly distinguish [1, 2] from [1] and [2]
Use a trie-like cache structure or composite keys

Examples

const add = memoize((a, b) => a + b);
add(1, 2); // 3 (computed)
add(1, 2); // 3 (cached)
add(2, 1); // 3 (computed — different args)

Solution

Reveal solution

function memoize(fn) {
  const cache = new Map();
  return function(...args) {
    let node = cache;
    for (const arg of args) {
      if (!node.has(arg)) node.set(arg, new Map());
      node = node.get(arg);
    }
    if (node.has('__result__')) return node.get('__result__');
    const result = fn(...args);
    node.set('__result__', result);
    return result;
  };
}

NameTopicDifficulty

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