memoized.ts

/*

Given a function fn, return a memoized version of that function.

A memoized function is a function that will never be called twice with the same inputs. Instead it will return a cached value.

You can assume there are 3 possible input functions: sum, fib, and factorial.

sum accepts two integers a and b and returns a + b.
fib accepts a single integer n and returns 1 if n <= 1 or fib(n - 1) + fib(n - 2) otherwise.
factorial accepts a single integer n and returns 1 if n <= 1 or factorial(n - 1) * n otherwise.

*/

type Fn = (...params: number[]) => number;

function memoize(fn: Fn): Fn {
  const results = new Map<string, number>();
  return function (...args: number[]): number {
    const key = JSON.stringify(args);
    const exists = results.has(key);

    if (exists) {
      return results.get(key) ?? -1;
    }

    const fnRes = fn(...args);

    results.set(key, fnRes);

    return fnRes;
  };
}

/**
 * let callCount = 0;
 * const memoizedFn = memoize(function (a, b) {
 *	 callCount += 1;
 *   return a + b;
 * })
 * memoizedFn(2, 3) // 5
 * memoizedFn(2, 3) // 5
 * console.log(callCount) // 1
 */