Memoize - Solution & Explanation

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. Assume that if a value has already been cached for the arguments (b, a) where a != b, it cannot be used for the arguments (a, b). For example, if the arguments are (3, 2) and (2, 3), two separate calls should be made.
• 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:
fnName = "sum"
actions = ["call","call","getCallCount","call","getCallCount"]
values = [[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); // "call" - returns 4. sum() was called as (2, 2) was not seen before.
memoizedSum(2, 2); // "call" - returns 4. However sum() was not called because the same inputs were seen before.
// "getCallCount" - total call count: 1
memoizedSum(1, 2); // "call" - returns 3. sum() was called as (1, 2) was not seen before.
// "getCallCount" - total call count: 2

Example 2:

Input:
fnName = "factorial"
actions = ["call","call","call","getCallCount","call","getCallCount"]
values = [[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); // "call" - returns 2.
memoFactorial(3); // "call" - returns 6.
memoFactorial(2); // "call" - returns 2. However factorial was not called because 2 was seen before.
// "getCallCount" - total call count: 2
memoFactorial(3); // "call" - returns 6. However factorial was not called because 3 was seen before.
// "getCallCount" - total call count: 2

Example 3:

Input:
fnName = "fib"
actions = ["call","getCallCount"]
values = [[5],[]]
Output: [8,1]
Explanation:
fib(5) = 8 // "call"
// "getCallCount" - total call count: 1

Constraints:

• 0 <= a, b <= 105
• 1 <= n <= 10
• 1 <= actions.length <= 105
• actions.length === values.length
• actions[i] is one of "call" and "getCallCount"
• fnName is one of "sum", "factorial" and "fib"