72 lines
1.8 KiB
JavaScript
72 lines
1.8 KiB
JavaScript
(() => {
|
|
|
|
// isHappy :: Int -> Bool
|
|
const isHappy = n => {
|
|
const f = n =>
|
|
foldl(
|
|
(a, x) => a + raise(read(x), 2), // ^2
|
|
0,
|
|
splitOn('', show(n))
|
|
),
|
|
p = (s, n) => n === 1 ? (
|
|
true
|
|
) : member(n, s) ? (
|
|
false
|
|
) : p(
|
|
insert(n, s), f(n)
|
|
);
|
|
return p(new Set(), n);
|
|
};
|
|
|
|
// GENERIC FUNCTIONS ------------------------------------------------------
|
|
|
|
// filter :: (a -> Bool) -> [a] -> [a]
|
|
const filter = (f, xs) => xs.filter(f);
|
|
|
|
// foldl :: (b -> a -> b) -> b -> [a] -> b
|
|
const foldl = (f, a, xs) => xs.reduce(f, a);
|
|
|
|
// insert :: Ord a => a -> Set a -> Set a
|
|
const insert = (e, s) => s.add(e);
|
|
|
|
// member :: Ord a => a -> Set a -> Bool
|
|
const member = (e, s) => s.has(e);
|
|
|
|
// read :: Read a => String -> a
|
|
const read = JSON.parse;
|
|
|
|
// show :: a -> String
|
|
const show = x => JSON.stringify(x);
|
|
|
|
// splitOn :: String -> String -> [String]
|
|
const splitOn = (cs, xs) => xs.split(cs);
|
|
|
|
// raise :: Num -> Int -> Num
|
|
const raise = (n, e) => Math.pow(n, e);
|
|
|
|
// until :: (a -> Bool) -> (a -> a) -> a -> a
|
|
const until = (p, f, x) => {
|
|
let v = x;
|
|
while (!p(v)) v = f(v);
|
|
return v;
|
|
};
|
|
|
|
// TEST -------------------------------------------------------------------
|
|
return show(
|
|
until(
|
|
m => m.xs.length === 8,
|
|
m => {
|
|
const n = m.n;
|
|
return {
|
|
n: n + 1,
|
|
xs: isHappy(n) ? m.xs.concat(n) : m.xs
|
|
};
|
|
}, {
|
|
n: 1,
|
|
xs: []
|
|
}
|
|
)
|
|
.xs
|
|
);
|
|
})();
|