Catalan numbers/Pascal's triangle: Difference between revisions
→{{header|JavaScript}}: ES6 ( by composition of generic functions )
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=={{header|JavaScript}}==
===ES5===
Iteration
{{trans|C++}}
<lang javascript>var n = 15;
Line 679 ⟶ 681:
1, 2, 5, 14, 42, 132, 429, 1430, 4862, 16796, 58786, 208012, 742900, 2674440, 9694845
</pre>
===ES6===
Functional composition
{{Trans|Haskell}}
<lang JavaScript>(() => {
'use strict';
// CATALAN
// catalan :: Int -> [Int]
let catalan = n => {
let alternate = xs => xs.reduce(
(a, x, i) => i % 2 === 0 ? a.concat([x]) : a, []
),
diff = xs => xs.length > 1 ? xs[0] - xs[1] : xs[0];
return tail(alternate(pascal((n + 1) * 2))
.map((xs, i) => diff(drop(i, xs))));
}
// PASCAL
// pascal :: Int -> [[Int]]
let pascal = n => until(
m => m.level <= 1,
m => {
let nxt = zipWith(
(a, b) => a + b, [0].concat(m.row), m.row.concat(0)
);
return {
row: nxt,
triangle: m.triangle.concat([nxt]),
level: m.level - 1
}
}, {
level: n,
row: [1],
triangle: [
[1]
]
}
)
.triangle;
// GENERIC FUNCTIONS
// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
let zipWith = (f, xs, ys) =>
xs.length === ys.length ? (
xs.map((x, i) => f(x, ys[i]))
) : undefined;
// until :: (a -> Bool) -> (a -> a) -> a -> a
let until = (p, f, x) => {
let v = x;
while (!p(v)) v = f(v);
return v;
}
// zip :: [a] -> [b] -> [(a,b)]
let zip = (xs, ys) =>
xs.length === ys.length ? (
xs.map((x, i) => [x, ys[i]])
) : undefined;
// Int -> [a] -> [a]
// Int -> String -> String
let drop = (n, xs) => xs.slice(n);
// tail :: [a] -> [a]
let tail = xs => xs.length ? xs.slice(1) : undefined;
return catalan(15);
})();</lang>
{{Out}}
<lang JavaScript>[1,2,5,14,42,132,429,1430,4862,16796,58786,208012,742900,2674440,9694845]</lang>
=={{header|jq}}==
| |||