2623. Memoize
Medium
265
18

Given a function `fn`, return a memoized version of that function.

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 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"]
[,,,[],,[]]
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"]
[,[]]
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`
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