2623. Memoize

Problem

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.

Example 1:

Input
"sum"
["call","call","getCallCount","call","getCallCount"]
[[2,2],[2,2],[],[1,2],[]]
Output
[4,4,1,3,2]

Explanation
const sum = (a, b) => a + b;
const memoizedSum = memoize(sum);
memoizedSum(2, 2); // Returns 4. sum() was called as (2, 2) was not seen before.
memoizedSum(2, 2); // Returns 4. However sum() was not called because the same inputs were seen before.
// Total call count: 1
memoizedSum(1, 2); // Returns 3. sum() was called as (1, 2) was not seen before.
// Total call count: 2

Example 2:

Input
"factorial"
["call","call","call","getCallCount","call","getCallCount"]
[[2],[3],[2],[],[3],[]]
Output
[2,6,2,2,6,2]

Explanation
const factorial = (n) => (n <= 1) ? 1 : (n * factorial(n - 1));
const memoFactorial = memoize(factorial);
memoFactorial(2); // Returns 2.
memoFactorial(3); // Returns 6.
memoFactorial(2); // Returns 2. However factorial was not called because 2 was seen before.
// Total call count: 2
memoFactorial(3); // Returns 6. However factorial was not called because 3 was seen before.
// Total call count: 2

Example 3:

Input
"fib"
["call","getCallCount"]
[[5],[]]
Output
[8,1]

Explanation
fib(5) = 8
// Total call count: 1

Constraints:

• 0 <= a, b <= 105
• 1 <= n <= 10
• at most 105 function calls
• at most 105 attempts to access callCount
• input function is sum, fib, or factorial

Solution (Javascript)

/**
 * @param {Function} fn
 */
function memoize(fn) {
  const cache = {};

  return function (...args) {
    const key = JSON.stringify(args);

    if (key in cache) {
      return cache[key];
    }

    const result = fn.apply(this, args);
    cache[key] = result;

    return result;
  };
}

const memoizedSum = memoize(function (a, b) {
  return a + b;
});

console.log(memoizedSum(2, 3)); // Output: Computing sum, 5
console.log(memoizedSum(2, 3)); // Output: 5

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).