Rep-string: Difference between revisions

=={{header|F_Sharp|F#}}==

<lang fsharp>let isPrefix p (s : string) = s.StartsWith(p)

let getPrefix n (s : string) = s.Substring(0,n)

let repPrefixOf str =

let rec isRepeatedPrefix p s =

if isPrefix p s then isRepeatedPrefix p (s.Substring (p.Length))

else isPrefix s p

let rec getLongestRepeatedPrefix n =

if n = 0 then None

elif isRepeatedPrefix (getPrefix n str) str then Some(getPrefix n str)

else getLongestRepeatedPrefix (n-1)

getLongestRepeatedPrefix (str.Length/2)

[<EntryPoint>]

let main argv =

printfn "Testing for rep-string (and showing the longest repeated prefix in case):"

[

"1001110011"

"1110111011"

"0010010010"

"1010101010"

"1111111111"

"0100101101"

"0100100"

"101"

"11"

"00"

"1"

] |>

List.map (fun s ->

match repPrefixOf s with | None -> s + ": NO" | Some(p) -> s + ": YES ("+ p + ")")

|> List.iter (printfn "%s")

0</lang>

{{out}}

<pre>Testing for rep-string (and showing the longest repeated prefix in case):

1001110011: YES (10011)

1110111011: YES (1110)

0010010010: YES (001)

1010101010: YES (1010)

1111111111: YES (11111)

0100101101: NO

0100100: YES (010)

101: NO

11: YES (1)

00: YES (0)

1: NO</pre>