Apa iku memoization lan piye carane ngleksanakan?

Question

Accepted Answer

**Memoization** nyimpan asil fungsi kanthi kunci saka argumen-argumenipun, supaya panggilan berulang kanthi input sing padha bali asil sing dicacat langsung tinimbang ngitung maneh. Iku nukar **memori kanggo kecepatan** lan mung gawe kanggo fungsi **pure** (input padha → asil padha, tanpa efek samping).

## Wadah memoize sing umum

```js
function memoize(fn) {
  const cache = new Map();
  return (...args) => {
    const key = JSON.stringify(args); // build a cache key from the arguments
    if (cache.has(key)) {
      return cache.get(key);          // cache hit — skip the work
    }
    const result = fn(...args);
    cache.set(key, result);
    return result;
  };
}

const slowSquare = n => { /* expensive */ return n * n; };
const fastSquare = memoize(slowSquare);
fastSquare(4); // computes → 16
fastSquare(4); // cached → 16 instantly
```

## Menang klasik: Fibonacci rekursif

```js
const fib = memoize(n => (n < 2 ? n : fib(n - 1) + fib(n - 2)));
// turns exponential O(2^n) into roughly O(n) by caching subproblems
```

## Trade-off lan peringatan

- **Strategi kunci cache**: `JSON.stringify` gagal kanggo fungsi, lan urutan kunci penting kanggo obyek. Kanggo argumen obyek, `WeakMap` (dikunci kanthi referensi) nyegah bocor memori.
- **Pertumbuhan tanpa batas**: cache ora tau menyusut — gunakake cache **LRU** kanggo proses dawa.
- Mung memoize nalika perhitungan ulang siyosake larang lan input bali.

## Mengapa iku penting

Memoization ana ngono-ngono: `useMemo`/`React.memo` React, selector Reselect, dynamic programming.

Konsep-ipun (cache asil pure miturut input) padha; seni-ipun milih kunci lan mbatesi cache.