Memoize – 2623

🔗LC2623 🟡 Medium 🧩 Pattern – Function Transformations

📅 Day 11/30 Days of JavaScript

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.

• sumaccepts 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.
• fibaccepts 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

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

Solution

This is similar to React.useMemo in React which is used to prevent expensive computations between renders and repetitive function calls.

/**
 * @param {Function} fn
 * @return {Function}
 */
function memoize(fn) {
    const cache = {};
    return function (...args) {
        const key = String(args);
        if (key in cache) {
            return cache[key];
        } else {
            const result = fn(...args)
            cache[key] = result;
            return result;
        }
    }
}

/** 
 * let callCount = 0;
 * const memoizedFn = memoize(function (a, b) {
 *	 callCount += 1;
 *   return a + b;
 * })
 * memoizedFn(2, 3) // 5
 * memoizedFn(2, 3) // 5
 * console.log(callCount) // 1 
 */