76 lines
2.0 KiB
Markdown
76 lines
2.0 KiB
Markdown
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---
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title: Averages-Pythagorean means
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---
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# Averages-Pythagorean means
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---
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## Solutions
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<details><summary>Solution 1 (Click to Show/Hide)</summary>
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```javascript
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function pythagoreanMeans(rangeArr) {
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// arithmeticMean :: [Number] -> Number
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const arithmeticMean = xs =>
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foldl((sum, n) => sum + n, 0, xs) / length(xs);
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// geometricMean :: [Number] -> Number
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const geometricMean = xs =>
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raise(foldl((product, x) => product * x, 1, xs), 1 / length(xs));
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// harmonicMean :: [Number] -> Number
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const harmonicMean = xs =>
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length(xs) / foldl((invSum, n) => invSum + (1 / n), 0, xs);
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// GENERIC FUNCTIONS ------------------------------------------------------
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// A list of functions applied to a list of arguments
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// <*> :: [(a -> b)] -> [a] -> [b]
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const ap = (fs, xs) => //
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Array.prototype.concat(...fs.map(f => //
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Array.prototype.concat(...xs.map(x => [f(x)]))));
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// foldl :: (b -> a -> b) -> b -> [a] -> b
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const foldl = (f, a, xs) => xs.reduce(f, a);
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// length :: [a] -> Int
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const length = xs => xs.length;
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// mapFromList :: [(k, v)] -> Dictionary
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const mapFromList = kvs =>
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foldl((a, [k, v]) =>
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(a[(typeof k === 'string' && k)] = v, a), {}, kvs);
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// raise :: Num -> Int -> Num
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const raise = (n, e) => Math.pow(n, e);
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/*
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// show :: a -> String
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// show :: a -> Int -> String
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const show = (...x) =>
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JSON.stringify.apply(
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null, x.length > 1 ? [x[0], null, x[1]] : x
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);
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*/
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// zip :: [a] -> [b] -> [(a,b)]
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const zip = (xs, ys) =>
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xs.slice(0, Math.min(xs.length, ys.length))
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.map((x, i) => [x, ys[i]]);
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// TEST -------------------------------------------------------------------
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// mean :: Dictionary
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const mean = mapFromList(zip(
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['Arithmetic', 'Geometric', 'Harmonic'],
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ap([arithmeticMean, geometricMean, harmonicMean], [
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rangeArr
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])
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));
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return {
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values: mean,
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test: `is A >= G >= H ? ${mean.Arithmetic >= mean.Geometric &&
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mean.Geometric >= mean.Harmonic ? 'yes' : 'no'}`
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};
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}
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```
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</details>
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