Longest run of a character in a string

Question

Your challenge: Write a function that takes a string s, a character c, and finds the length of the longest run of c in s. The length of the run will be l.

Rules:

• If s is of length 0 or c is empty, l should be 0.
• If there are no instances of c in s, l should be 0.
• Standard loopholes and Standard I/O Rules apply.
• No matter where in s the run of cs is located, l should be the same.
• Any printable ASCII characters can appear in s and c.

Test cases:

s,c --> l
"Hello, World!",'l'  -->  2
"Foobar",'o'         -->  2
"abcdef",'e'         -->  1
"three   spaces",' ' -->  3
"xxx xxxx xx",'x'    -->  4
"xxxx xx xxx",'x'    -->  4
"",'a'               -->  0
"anything",''        -->  0

Winner:

As with code-golf the shortest answer in each language wins.

Answer 1

Zsh, 18 bytes

tr -c $1 \\n|wc -L

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Explanation:

• tr: translate characters in STDIN:
  • -c: replace all except
  • $1: the first command-line argument
  • \\n: with newlines
• |wc -L: then output the length of the longest line

Answer 2

K (ngn/k), 11 bytes

Takes arguments in swapped order.

#1_|':\1,^?

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^? for each character in s, is it not a member of c?
1, prepend 1.
|':\ until the value stops changing, do pairwise or. This shrinks each run of 0s by 1 per iteration. Collects all intermediate results.
1_ Drop the first value (the initial boolean vector).
# Length. Counts the number of steps it took to fill the vector with 1s.

If we wouldn't have to deal with empty c, this could be 10 bytes instead:

#1_&':\0,=

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Answer 3

Jelly, 5 bytes

=Œg§Ṁ

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-3 bytes thanks to Unrelated String. Port of my Vyxal answer.

This takes a literal character, which can't be input (Jelly treats strings as char arrays), so the footer converts the single-character string into a character. The link can also be called this way.

=     # Is each char of the string equal to the given character?
 Œg   # Group consecutive identical items
   §  # Sum each
    Ṁ # Get the maximum

Answer 4

Jelly, 5 bytes

ṁ¹ẇƤS

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Takes a character on the left and the string on the right. Can also take the character as a length-1 string (and thus be run as a full program), but errors if given a length-0 string, so it's unclear if this is valid given input that way due to one of the most confusing comment clarifications in site history.

ṁ        Mold the character to the length of the string,
 ¹       then
   Ƥ     for each prefix of that result
  ẇ      test if it's a contiguous substring of the string.
    S    Count up how many are.

Answer 5

Ruby, 40 bytes

->s,c{s.split(%r{[^#{c}]}).max&.size||0}

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Answer 6

Clojure, 56 bytes

#(apply max(reductions(fn[r c](if(= c %2)(inc r)0))0 %))

Answer 7

Arturo, 31 bytes

$[s c]->size max match s~{|c|+}

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Answer 8

J, 17 bytes

[:>./0(+/;.1)@,e.

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[:>./0(+/;.1)@,e.
[:                NB. enforces f(g(y))
     0(+/;.1)@,e. NB. g
               e. NB. check if each char of x is equal to y
     0        ,   NB. prepend a 0
             @    NB. then
      (+/;.1)     NB. cutting and summing
         ;.1      NB. cut up array using first item as delimiter, groups runs of 1's
       +/         NB. sum to get count
  >./             NB. f, get max of result

Answer 9

Japt, 9 bytes

ôÀV mÊrwT

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Answer 10

Lua, 89 bytes

s,c=...a=0s:gsub(c:gsub('%W','%%%1')..'+',load'a=math.max(#...,a)')print(#c==0 and 0or a)

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Ungolfed version:

s,c=...                           --Take s and c as program arguments
a=0                               --a stores max run of c
s:gsub(c:gsub('%W','%%%1')..'+',  --For every run of c
load'a=math.max(#...,a)')         --If length of c is longer than a, put into a
print(#c==0 and 0or a)            --If c is 0, print 0, otherwise print a

Answer 11

Scala, 98 bytes

Golfed version. Try it online!

def f(c:Char,s:String)=s.foldLeft((0,0)){case((d,m),x)=>if(x==c)(d+1,Math.max(d+1,m))else(0,m)}._2

Ungolfed version. Try it online!

object Main {
  def f(c: Char, s: String): Int = s.foldLeft((0, 0)) {
    case ((count, maxCount), char) =>
      if (char == c) (count + 1, Math.max(count + 1, maxCount))
      else (0, maxCount)
  }._2

  def main(args: Array[String]): Unit = {
    println(f('c', "ccc cccc cc"))
    println(f('c', ""))
    println(f('c', "abcdef"))
  }
}

Answer 12

Thunno 2 G, 3 bytes

=ġʂ

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Port of Adnan's 05AB1E answer.

Explanation

=ġʂ  # Implicit input
=    # For each character, does it equal the second input?
 ġ   # Group consecutive equal items together
  ʂ  # Sum each inner list
     # Implicit output of maximum