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Merge pull request TheAlgorithms#732 from MrDoomy/feat/memoize-func

Feat: Added Memoize Func

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	`1`	`+/**`
	`2`	`+ * Memoize`
	`3`	`+ *`
	`4`	`+ * From [Wikipedia](https://en.wikipedia.org/wiki/Memoization),`
	`5`	`+ * memoization is an optimization technique`
	`6`	`+ * used primarily to speed up computer programs,`
	`7`	`+ * by storing the results of expensive function calls`
	`8`	`+ * and returning the cached result when the same inputs occur again`
	`9`	`+ *`
	`10`	`+ * This function is a first class objects,`
	`11`	`+ * which lets us use it as [Higher-Order Function](https://eloquentjavascript.net/05_higher_order.html)`
	`12`	`+ * and return another function`
	`13`	`+ *`
	`14`	`+ * @param {Function} func Original function`
	`15`	`+ * @returns {Function} Memoized function`
	`16`	`+ */`
	`17`	`+export const memoize = (func) => {`
	`18`	`+ // Initialization of a slot to store the function result`
	`19`	`+ const cache = {}`
	`20`	`+`
	`21`	`+ return (...args) => {`
	`22`	`+ // Retrieving the first argument of the function`
	`23`	`+ const [arg] = args`
	`24`	`+`
	`25`	`+ /**`
	`26`	`+ * Checks if the argument is already present in the cache,`
	`27`	`+ * then return the associated value / result`
	`28`	`+ */`
	`29`	`+ if (arg in cache) {`
	`30`	`+ return cache[arg]`
	`31`	`+ }`
	`32`	`+`
	`33`	`+ /**`
	`34`	`+ * If the argument is not yet present in the cache,`
	`35`	`+ * execute original function and save its value / result in cache,`
	`36`	`+ * finally return it`
	`37`	`+ */`
	`38`	`+ const result = func(arg)`
	`39`	`+ cache[arg] = result`
	`40`	`+ return result`
	`41`	`+ }`
	`42`	`+}`

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	`1`	`+import { memoize } from '../Memoize'`
	`2`	`+`
	`3`	`+const fibonacci = (n) => {`
	`4`	`+ if (n < 2) {`
	`5`	`+ return n`
	`6`	`+ }`
	`7`	`+`
	`8`	`+ return fibonacci(n - 2) + fibonacci(n - 1)`
	`9`	`+}`
	`10`	`+`
	`11`	`+const factorial = (n) => {`
	`12`	`+ if (n === 0) {`
	`13`	`+ return 1`
	`14`	`+ }`
	`15`	`+`
	`16`	`+ return n * factorial(n - 1)`
	`17`	`+}`
	`18`	`+`
	`19`	`+describe('Memoize', () => {`
	`20`	`+ it('expects the fibonacci function to use the cache on the second call', () => {`
	`21`	`+ const memoFibonacci = memoize(fibonacci)`
	`22`	`+`
	`23`	`+ expect(memoFibonacci(5)).toEqual(fibonacci(5))`
	`24`	`+ expect(memoFibonacci(5)).toEqual(5)`
	`25`	`+ expect(memoFibonacci(10)).toEqual(fibonacci(10))`
	`26`	`+ expect(memoFibonacci(10)).toEqual(55)`
	`27`	`+ })`
	`28`	`+`
	`29`	`+ it('expects the factorial function to use the cache on the second call', () => {`
	`30`	`+ const memoFactorial = memoize(factorial)`
	`31`	`+`
	`32`	`+ expect(memoFactorial(5)).toEqual(factorial(5))`
	`33`	`+ expect(memoFactorial(5)).toEqual(120)`
	`34`	`+ expect(memoFactorial(10)).toEqual(factorial(10))`
	`35`	`+ expect(memoFactorial(10)).toEqual(3628800)`
	`36`	`+ })`
	`37`	`+})`

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