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: 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 0 <= actions.length <= 105 actions.length === values.length actions[i] is one of “call” and “getCallCount” fnName is one of “sum”, “factorial” and ”fib”

Pre analysis

This is typical memoize problem, we will keep a map of function name and its arguments and return value. If function is called again with same arguments, we will return the value from map. To generate key, we will use JSON.stringify on arguments.