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