merge: Improved Memoize function (#912)

* feat: improved memoize function

used Map instead of object & used the JSON.stringfy method for generate a valid string as a key

* docs: modified documentation

* style: format with standard

* docs: modified stringify doc

* refactor: remove two repetition implementation

Author: fahimfaisaal

Cache/Memoize.js

@@ -1,42 +1,60 @@
 /**
- * Memoize
- *
+ * @function memoize
+ * @description ->
  * From [Wikipedia](https://en.wikipedia.org/wiki/Memoization),
  * memoization is an optimization technique
  * used primarily to speed up computer programs,
  * by storing the results of expensive function calls
  * and returning the cached result when the same inputs occur again
- *
  * This function is a first class objects,
  * which lets us use it as [Higher-Order Function](https://eloquentjavascript.net/05_higher_order.html)
  * and return another function
- *
  * @param {Function} func Original function
  * @returns {Function} Memoized function
  */
-export const memoize = (func) => {
-  // Initialization of a slot to store the function result
-  const cache = {}
+const memoize = (func) => {
+  // Initialization of a slot to store the function result by arguments as a key in Hash Map
+  const cache = new Map()
+
+  const jsonReplacer = (_, value) => {
+    if (value instanceof Set) { // if the value is Set it's converted to Array cause JSON.stringify can't convert Set
+      return [...value]
+    }
+
+    if (value instanceof Map) { // if the value is Map it's converted to Object cause JSON.stringify can't convert Map
+      return Object.fromEntries(value)
+    }
+
+    return value
+  }
 
   return (...args) => {
-    // Retrieving the first argument of the function
-    const [arg] = args
+    /**
+     * Arguments converted to JSON string for use as a key of Map - it's easy to detect collections like -> Object and Array
+     * If the args input is -> [new Set([1, 2, 3, 4]), {name: 'myName', age: 23}]
+     * Then the agrsKey generate to -> '[[1,2,3,4],{"name":"myName","age":23}]' which is JSON mean string
+     * Now it's ready to be a perfect key for Map
+     */
+    const argsKey = JSON.stringify(args, jsonReplacer)
 
     /**
      * Checks if the argument is already present in the cache,
      * then return the associated value / result
      */
-    if (arg in cache) {
-      return cache[arg]
+    if (cache.has(argsKey)) {
+      return cache.get(argsKey)
     }
 
     /**
      * If the argument is not yet present in the cache,
      * execute original function and save its value / result in cache,
      * finally return it
      */
-    const result = func(arg)
-    cache[arg] = result
+    const result = func(...args) // spread all args
+    cache.set(argsKey, result)
+
     return result
   }
 }
+
+export { memoize }

Cache/test/Memoize.test.js

@@ -1,22 +1,21 @@
 import { memoize } from '../Memoize'
+import { fibonacci } from '../../Dynamic-Programming/FibonacciNumber'
+import { factorial } from '../../Recursive/Factorial'
 
-const fibonacci = (n) => {
-  if (n < 2) {
-    return n
-  }
+const multipleFactorials = (arr) => arr.map(factorial)
 
-  return fibonacci(n - 2) + fibonacci(n - 1)
+/**
+ * @title implementation of union function
+ * @param {Set} sets
+ * @return {new Set}
+ */
+function union (...sets) {
+  return new Set(
+    sets.reduce((flatArray, set) => [...flatArray, ...set], [])
+  )
 }
 
-const factorial = (n) => {
-  if (n === 0) {
-    return 1
-  }
-
-  return n * factorial(n - 1)
-}
-
-describe('Memoize', () => {
+describe('Testing Memoize', () => {
   it('expects the fibonacci function to use the cache on the second call', () => {
     const memoFibonacci = memoize(fibonacci)
 
@@ -34,4 +33,32 @@ describe('Memoize', () => {
     expect(memoFactorial(10)).toEqual(factorial(10))
     expect(memoFactorial(10)).toEqual(3628800)
   })
+
+  it('expects the multipleFactorials function to use the cache on the second call', () => {
+    const memoMultipleFactorials = memoize(multipleFactorials)
+    const input = [2, 3, 4, 5]
+
+    expect(memoMultipleFactorials(input)).toEqual([2, 6, 24, 120])
+    expect(memoMultipleFactorials(input)).toEqual(multipleFactorials(input))
+  })
+
+  it('expects the multipleFactorials function to use the cache on the second call', () => {
+    const memoMultipleFactorials = memoize(multipleFactorials)
+    const input = [2, 3, 4, 5]
+
+    expect(memoMultipleFactorials(input)).toEqual([2, 6, 24, 120])
+    expect(memoMultipleFactorials(input)).toEqual(multipleFactorials(input))
+  })
+
+  it('expects the union function to use the cache on the second call', () => {
+    const memoUnion = memoize(union)
+    const inputs = [
+      new Set([1, 2, 3]),
+      new Set([4, 3, 2]),
+      new Set([5, 3, 6])
+    ]
+
+    expect(memoUnion(...inputs)).toEqual(new Set([1, 2, 3, 4, 5, 6]))
+    expect(memoUnion(...inputs)).toEqual(union(...inputs))
+  })
 })