g2601_2700.s2630_memoize_ii.readme.md Maven / Gradle / Ivy

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2630\. Memoize II

Hard

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.

`fn` can be any function and there are no constraints on what type of values it accepts. Inputs are considered identical if they are `===` to each other.

**Example 1:**

**Input:** 

getInputs = () => [[2,2],[2,2],[1,2]] 

fn = function (a, b) { return a + b; }

**Output:** [{"val":4,"calls":1},{"val":4,"calls":1},{"val":3,"calls":2}]

**Explanation:** 

    const inputs = getInputs(); 
    const memoized = memoize(fn); 
    for (const arr of inputs) { 
        memoized(...arr); 
    } 

For the inputs of (2, 2): 2 + 2 = 4, and it required a call to fn(). 

For the inputs of (2, 2): 2 + 2 = 4, but those inputs were seen before so no call to fn() was required. 

For the inputs of (1, 2): 1 + 2 = 3, and it required another call to fn() for a total of 2.

**Example 2:**

**Input:** 

getInputs = () => [[{},{}],[{},{}],[{},{}]] 

fn = function (a, b) { return ({...a, ...b}); }

**Output:** [{"val":{},"calls":1},{"val":{},"calls":2},{"val":{},"calls":3}]

**Explanation:** Merging two empty objects will always result in an empty object. It may seem like there should only be 1 call to fn() because of cache-hits, however none of those objects are === to each other.

**Example 3:**

**Input:** 

getInputs = () => { const o = {}; return [[o,o],[o,o],[o,o]]; } 

fn = function (a, b) { return ({...a, ...b}); }

**Output:** [{"val":{},"calls":1},{"val":{},"calls":1},{"val":{},"calls":1}]

**Explanation:** Merging two empty objects will always result in an empty object. The 2nd and 3rd third function calls result in a cache-hit. This is because every object passed in is identical.

**Constraints:**

*   1 <= inputs.length <= 10⁵
*   0 <= inputs.flat().length <= 10⁵
*   `inputs[i][j] != NaN`