2623-memoize

2623. Memoize (Medium) (https://leetcode.com/problems/memoize)

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.

type Fn = (...params: number[]) => number
 
function memoize(fn: Fn): Fn {
  const cache = new Map<string, number>()
 
  return function (...args) {
    const key = JSON.stringify(args)
 
    if (!cache.has(key)) {
      cache.set(key, fn(...args))
    }
 
    return cache.get(key)!
  }
}
 
let callCount = 0
const memoizedFn = memoize((a, b) => {
  callCount += 1
  return a + b
})
console.log(memoizedFn(2, 3)) // 5
console.log(memoizedFn(2, 3)) // 5
console.log(callCount) // 1

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],[]]
 
<!-- [[leetcode/untagged]] [[leetcode/untagged/2622-cache-with-time-limit]] [[leetcode/untagged/2626-array-reduce-transformation]] -->
    Output: [2,6,2,2,6,2]
    Explanation:
    const factorial = (n) => (n <= 1) ? 1 : (nfactorial(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