[Object] Memoize (feat. JSON.stringyfy)

https://leetcode.com/problems/memoize/description/

Memoize - LeetCode

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
"sum"
["call","call","getCallCount","call","getCallCount"]
[[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); // Returns 4. sum() was called as (2, 2) was not seen before.
memoizedSum(2, 2); // Returns 4. However sum() was not called because the same inputs were seen before.
// Total call count: 1
memoizedSum(1, 2); // Returns 3. sum() was called as (1, 2) was not seen before.
// Total call count: 2

Example 2:

Input
"factorial"
["call","call","call","getCallCount","call","getCallCount"]
[[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); // Returns 2.
memoFactorial(3); // Returns 6.
memoFactorial(2); // Returns 2. However factorial was not called because 2 was seen before.
// Total call count: 2
memoFactorial(3); // Returns 6. However factorial was not called because 3 was seen before.
// Total call count: 2

Example 3:

Input
"fib"
["call","getCallCount"]
[[5],[]]
Output
[8,1]

Explanation
fib(5) = 8
// Total call count: 1

 

Constraints:

• 0 <= a, b <= 105
• 1 <= n <= 10
• at most 105 function calls
• at most 105 attempts to access callCount
• input function is sum, fib, or factorial

 

solution

/**
 * @param {Function} fn
 */
function memoize(fn) {
    const memoObj = {};
    return function(...args) {
        const key = JSON.stringify(args);
        if(memoObj[key] === undefined) {
            memoObj[key] = fn(...args);
        }
        return memoObj[key];
    }
}


/** 
 * 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 
 */

key값으로 arg로 바로 저장하지 않고 JSON.stringify를 이용하여 string type으로 변환하여 key 값으로 저장하는 게 속도가 더 빠름