2623. Memoize

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2623. Memoize

題目描述

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.

範例

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

解答

TypeScript

type Fn = (...params: any) => any;

function memoize(fn: Fn): Fn {
  const map = new Map();

  return (...args) => {
    const paramsKey = JSON.stringify(args);
    if (map.has(paramsKey)) {
      return map.get(paramsKey);
    }

    map.set(paramsKey, fn(...args));
    return map.get(paramsKey);
  };
}

// one liner
const memoize = (fn: Fn, cache = {}): Fn => (...args) => (cache[args.join()] = cache[args.join()] ?? fn(...args));

SheepSat, May 13, 2023

Reference

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