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Ingy döt Net 2023-07-01 11:58:00 -04:00
parent 72d218235f
commit f23f22d71c
199087 changed files with 3378941 additions and 0 deletions

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<html><head><title>Catalan</title></head>
<body><pre id='x'></pre><script type="application/javascript">
function disp(x) {
var e = document.createTextNode(x + '\n');
document.getElementById('x').appendChild(e);
}
var fc = [], c2 = [], c3 = [];
function fact(n) { return fc[n] ? fc[n] : fc[n] = (n ? n * fact(n - 1) : 1); }
function cata1(n) { return Math.floor(fact(2 * n) / fact(n + 1) / fact(n) + .5); }
function cata2(n) {
if (n == 0) return 1;
if (!c2[n]) {
var s = 0;
for (var i = 0; i < n; i++) s += cata2(i) * cata2(n - i - 1);
c2[n] = s;
}
return c2[n];
}
function cata3(n) {
if (n == 0) return 1;
return c3[n] ? c3[n] : c3[n] = (4 * n - 2) * cata3(n - 1) / (n + 1);
}
disp(" meth1 meth2 meth3");
for (var i = 0; i <= 15; i++)
disp(i + '\t' + cata1(i) + '\t' + cata2(i) + '\t' + cata3(i));
</script></body></html>

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(() => {
"use strict";
// ----------------- CATALAN NUMBERS -----------------
// catalansDefinitionThree :: [Int]
const catalansDefinitionThree = () =>
// An infinite sequence of Catalan numbers.
scanlGen(
c => n => Math.floor(
(2 * c * pred(2 * n)) / succ(n)
)
)(1)(
enumFrom(1)
);
// ---------------------- TEST -----------------------
// main :: IO ()
const main = () =>
take(15)(
catalansDefinitionThree()
);
// --------------------- GENERIC ---------------------
// enumFrom :: Enum a => a -> [a]
const enumFrom = function* (n) {
// An infinite sequence of integers,
// starting with n.
let v = n;
while (true) {
yield v;
v = 1 + v;
}
};
// pred :: Int -> Int
const pred = x =>
x - 1;
// scanlGen :: (b -> a -> b) -> b -> Gen [a] -> [b]
const scanlGen = f =>
// The series of interim values arising
// from a catamorphism over an infinite list.
startValue => function* (gen) {
let
a = startValue,
x = gen.next();
yield a;
while (!x.done) {
a = f(a)(x.value);
yield a;
x = gen.next();
}
};
// succ :: Int -> Int
const succ = x =>
1 + x;
// take :: Int -> [a] -> [a]
// take :: Int -> String -> String
const take = n =>
// The first n elements of a list,
// string of characters, or stream.
xs => Array.from({
length: n
}, () => {
const x = xs.next();
return x.done ? [] : [x.value];
}).flat();
// MAIN ---
return JSON.stringify(main(), null, 2);
})();