61 lines
1.6 KiB
JavaScript
61 lines
1.6 KiB
JavaScript
(() => {
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// isHappy :: Int -> Bool
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const isHappy = n => {
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const f = n =>
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foldl(
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(a, x) => a + raise(read(x), 2), // ^2
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0,
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splitOn('', show(n))
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),
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p = (s, n) => n === 1 ? (
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true
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) : member(n, s) ? (
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false
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) : p(
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insert(n, s), f(n)
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);
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return p(new Set(), n);
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};
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// GENERIC FUNCTIONS ------------------------------------------------------
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// enumFromTo :: Int -> Int -> [Int]
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const enumFromTo = (m, n) =>
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Array.from({
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length: Math.floor(n - m) + 1
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}, (_, i) => m + i);
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// filter :: (a -> Bool) -> [a] -> [a]
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const filter = (f, xs) => xs.filter(f);
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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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// insert :: Ord a => a -> Set a -> Set a
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const insert = (e, s) => s.add(e);
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// member :: Ord a => a -> Set a -> Bool
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const member = (e, s) => s.has(e);
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// read :: Read a => String -> a
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const read = JSON.parse;
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// show :: a -> String
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const show = x => JSON.stringify(x);
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// splitOn :: String -> String -> [String]
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const splitOn = (cs, xs) => xs.split(cs);
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// raise :: Num -> Int -> Num
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const raise = (n, e) => Math.pow(n, e);
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// take :: Int -> [a] -> [a]
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const take = (n, xs) => xs.slice(0, n);
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// TEST -------------------------------------------------------------------
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return show(
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take(8, filter(isHappy, enumFromTo(1, 50)))
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);
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})()
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