Factorial: Difference between revisions
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===Imperative=== |
===Imperative=== |
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An imperative style using a mutable variable: |
An imperative style using a mutable variable: |
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<syntaxhighlight lang="scala"> |
<syntaxhighlight lang="scala"> |
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def factorial(n: Int) = { |
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var res = 1 |
var res = 1 |
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for (i <- 1 to n) |
for (i <- 1 to n) |
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res *= i |
res *= i |
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res |
res |
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} |
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</syntaxhighlight> |
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===Recursive=== |
===Recursive=== |
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Using naive recursion: |
Using naive recursion: |
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<syntaxhighlight lang="scala"> |
<syntaxhighlight lang="scala"> |
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def factorial(n: Int): Int = |
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if (n < 1) 1 |
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else n * factorial(n - 1) |
else n * factorial(n - 1) |
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Using tail recursion with a helper function: |
Using tail recursion with a helper function: |
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<syntaxhighlight lang="scala"> |
<syntaxhighlight lang="scala"> |
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def factorial(n: Int) = { |
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@tailrec def fact(x: Int, acc: Int): Int = { |
@tailrec def fact(x: Int, acc: Int): Int = { |
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if (x < 2) acc else fact(x - 1, acc * x) |
if (x < 2) acc else fact(x - 1, acc * x) |
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} |
} |
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fact(n, 1) |
fact(n, 1) |
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} |
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| ⚫ | |||
| ⚫ | |||
===Stdlib .product=== |
===Stdlib .product=== |
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===Folding=== |
===Folding=== |
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Using folding: |
Using folding: |
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<syntaxhighlight lang="scala"> |
<syntaxhighlight lang="scala"> |
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def factorial(n: Int) = |
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(2 to n).foldLeft(1)(_ * _) |
(2 to n).foldLeft(1)(_ * _) |
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</syntaxhighlight> |
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===Using implicit functions to extend the Int type=== |
===Using implicit functions to extend the Int type=== |
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Enriching the integer type to support unary exclamation mark operator and implicit conversion to big integer: |
Enriching the integer type to support unary exclamation mark operator and implicit conversion to big integer: |
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<syntaxhighlight lang="scala"> |
<syntaxhighlight lang="scala"> |
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implicit def IntToFac(i : Int) = new { |
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def ! = (2 to i).foldLeft(BigInt(1))(_ * _) |
def ! = (2 to i).foldLeft(BigInt(1))(_ * _) |
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} |
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</syntaxhighlight> |
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{{out | Example used in the REPL}} |
{{out | Example used in the REPL}} |
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