# Find the highest unique digit

Surprisingly we haven't had a simple "find the highest digit" challenge yet, but I think that's a little too trivial.

Given input of a non-negative integer, return the highest unique (ie not repeated) digit found in the integer. If there are no unique digits, your program can do anything (undefined behaviour).

The input can be taken as a single integer, a string, or a list of digits.

## Test cases

12         -> 2
0          -> 0
485902     -> 9
495902     -> 5
999999     -> Anything
999099     -> 0
1948710498 -> 7


This is so fewest bytes in each language wins!

• Can we take input as a string instead? – user41805 Jun 28 '17 at 8:13
• Given the last test case, I think we are forced to take input as a string... (leading zeroes can't be represented in integers) – Leo Jun 28 '17 at 8:14
• @Leo that was my bad actually, basically mashed the numbers on my keyboard, didn't notice the leading zero. But yes, input can be taken as a string – Skidsdev Jun 28 '17 at 8:17
• @Adám "undefined behaviour" generally means you can do anything, including summoning nameless horrors from the void if that saves bytes. – Martin Ender Jun 28 '17 at 8:22
• @MartinEnder in fact I'll happily knock off 50% of your bytes if your code successfully summons cthulhu upon there being no unique digits ;) – Skidsdev Jun 28 '17 at 8:31

# 05AB1E, 4 3 bytes

Saved 1 byte thanks to Mr. Xcoder notifying that a digit list is valid input.

¢ÏM


Try it online!

Explanation

¢     # count occurrences of each digit in input
Ï    # keep only the digits whose occurrences are true (1)
M   # push the highest

• Wait so in 05AB1E, 2 is not truthy; only 1? :o – HyperNeutrino Jun 29 '17 at 2:05
• @HyperNeutrino: Correct! – Emigna Jun 29 '17 at 6:02
• That seems both very useful and very bothersome... That is interesting :o :D – HyperNeutrino Jun 29 '17 at 6:05
• @HyperNeutrino: It often comes in handy, but it can be a disadvantage when the challenge says return a truthy value, when a lot of languages can return any positive integer or maybe even a non-empty string. – Emigna Jun 29 '17 at 6:27
• A strikethrough on the number for is not easy to see! – MrZander Jun 29 '17 at 23:48

# Python 3, 40 bytes

Saved 2 bytes thanks to movatica.

lambda i:max(x*(i.count(x)<2)for x in i)


Try it online!

### 42 bytes

Works for both String and list of digits parameter types. Throws an error for no unique digits, kind of abuses of that spec:

lambda i:max(x for x in i if i.count(x)<2)


Try it online!

## Explanation

• lambda i: - Declares a lambda function with a string or list of digits parameter i.
• max(...) - Finds the maximum value of the generator.
• x for x in i - Iterates through the characters / digits of i.
• if i.count(x)<2 - Checks if the digit is unique.
• 40 bytes: lambda i:max(x*(i.count(x)<2)for x in i) – movatica May 21 '19 at 22:00
• @movatica Thanks! – Mr. Xcoder May 22 '19 at 4:52

## Alice, 15 bytes

/&.sDo
\i-.tN@/


Try it online!

### Explanation

/...
\.../


This is a simple framework for linear code that operates entirely in Ordinal mode (meaning this program works completely through string processing). The unfolded linear code is then just:

i..DN&-sto@


What it does:

i    Read all input as a string.
..   Make two copies.
D    Deduplicate the characters in the top copy.
N    Get the multiset complement of this deduplicated string in the input.
This gives us a string that only contains repeated digits (with one
copy less than the original, but the number of them doesn't matter).
&-   Fold string subtraction over this string, which means that each of
the repeated digits is removed from the input.
s    Sort the remaining digits.
t    Split off the last digit.
o    Print it.
@    Terminate the program.

• -1, doesn't "summoning nameless horrors from the void" if there are no unique digits. ;) (Read: +1, great answer as always.) – Kevin Cruijssen Jun 28 '17 at 13:46
• @KevinCruijssen I tried, but it didn't save bytes. Maybe Dark might be a more appropriate language... – Martin Ender Jun 28 '17 at 13:52

## Retina, 16 bytes

O.
(.)\1+

!.$ Try it online! ### Explanation O.  Sort the digits. (.)\1+  Remove repeated digits. !.$


Fetch the last (maximal) digit.

• Too bad Deduplicate doesn't help here :( – CalculatorFeline Jun 28 '17 at 19:53

# Charcoal, 18 12 bytes

Ｆχ¿⁼№θＩι¹ＰＩι


Try it online! (Link to verbose version)

Prints nothing if no solution is found. The trick is that the for loop prints every unique number in the input string, but without moving the cursor, thus the value keeps reprinting itself until the final solution is found.

The previous version printed the characters A to Z when no solution was found, hence the comments:

ＡααＦχＡ⎇⁼№θＩι¹Ｉιααα


Try it online! (Link to verbose version)

• That's an interesting undefined behavior :) – Emigna Jun 28 '17 at 8:42
• This sounds Finnish to me :D – fedorqui Jun 28 '17 at 9:33
• @fedorqui nice to see you here! Yeah, but Charcoal is easier to learn than Jelly or O5AB1E, and it's funnier to use in ASCII-art games. :-) – Charlie Jun 28 '17 at 9:37

# Husk, 7 bytes

→fo¬hgO


Try it online! (Test suite, crashes on the last test case since it has no unique digits)

This is a composition of functions in point-free style (the arguments are not mentioned explicitely anywhere). Takes input and returns output as a string, which in Husk is equivalent to a list of characters.

### Explanation

Test case: "1948710498"

O    Sort:                             "0114478899"
g     Group consecutive equal elements: ["0","11","44","7","88","99"]
fo¬h      Keep only those with length 1*:   ["0","7"]
→          Take the last element:            "7"


*The check for length 1 is done by taking the head of the list (all elements except the last one) and negating it (empty lists are falsy, non-empty lists are truthy).

f s=maximum[x|x<-s,[x]==filter(==x)s]


Try it online!

How it works:

  [  |x<-s   ]          -- loop x through the input string s
x                   -- and keep the x where
[x]==filter(==x)s  -- all x extracted from s equal a singleton list [x]
maximum                 -- take the maximum of all the x


# R, 41 bytes

function(x,y=table(x))max(names(y[y==1]))


An anonymous function that takes a list of digits, either as integers or single character strings. It precomputes y as an optional argument to avoid using curly braces for the function body. Returns the digit as a string. This takes a slightly different approach than the other R answer and ends up being the tiniest bit shorter! looks like my comment there was wrong after all...

table computes the occurrences of each element in the list, with names(table(x)) being the unique values in x (as strings). Since digits are fortunately ordered the same lexicographically as numerically, we can still use max.

Try it online!

• Nice! I didn't expect doing something with table would be shorter (plus I can never remember how to get names to work). – aPaulT Jun 28 '17 at 19:35
• <2 for another byte. There should never be a zero in the counts. – MickyT Jun 28 '17 at 20:28
• y=table(scan());max(names(y[y<2])) is a few bytes shorter. – JAD Jun 29 '17 at 8:53

## JavaScript (ES6), 4641 40 bytes

Takes input as a string. Returns RangeError if there are no unique digits.

s=>f=(i=9)=>s.split(i).length-2?f(--i):i


-7 bytes thanks to Rick Hitchcock

-1 byte thanks to Shaggy

### Test cases

let f =

s=>g=(i=9)=>s.split(i).length-2?g(--i):i

console.log(f("12")())         // 2
console.log(f("0")())          // 0
console.log(f("485902")())     // 9
console.log(f("495902")())     // 5
//console.log(f("999999")())   // RangeError
console.log(f("999099")())     // 0
console.log(f("1948710498")()) // 7

• Remove the alert for 39 bytes: (s,i=9)=>s.split(i).length-2?f(s,--i):i. You can avoid the stack overflow for 42 bytes: (s,i=9)=>s.split(i).length-2?i&&f(s,--i):i. – Rick Hitchcock Jun 28 '17 at 13:09
• Save a byte with currying: s=>g=(i=9)=>s.split(i).length-2?g(--i):i and then call it with f("12")() – Shaggy Jun 28 '17 at 14:08

# Python 3, 40 bytes

lambda i:max(x+9-9*i.count(x)for x in i)


Only works for lists of digits. The edge case '990' works fine :)

Try it online!

• Welcome to PPCG! Looks like you've got everything down :) – Stephen Jun 28 '17 at 23:29

# Brachylog, 8 bytes

ọtᵒtᵍhth


Try it online!

### Explanation

Example input: 495902

ọ          Occurences:    [[4,1],[9,2],[5,1],[0,1],[2,1]]
tᵒ        Order by tail: [[0,1],[2,1],[4,1],[5,1],[9,2]]
tᵍ      Group by tail: [[[0,1],[2,1],[4,1],[5,1]],[[9,2]]]
t    Tail:          [5,1]


## Husk, 9 8 bytes

Thanks to Leo for suggesting a slightly neater solution at the same byte count.

▲‡ȯf=1#


Try it online!

### Explanation

  ȯ       Compose the following thre functions into one binary function.
#  Count the occurrences of the right argument in the left.
=1    Check equality with 1. This gives 1 (truthy) for values that
appear uniquely in the right-hand argument.
f      Select the elements from the right argument, where the function
in the left argument is truthy.
Due to the composition and partial function application this
means that the first argument of the resulting function actually
curries # and the second argument is passed as the second
argument to f. So what we end up with is a function which selects
the elements from the right argument that appear uniquely in
the left argument.
‡        We call this function by giving it the input for both arguments.
So we end up selecting unique digits from the input.
▲         Find the maximum.

• ¬← could be more simply =1, same bytecount though :) – Leo Jun 28 '17 at 9:08
• @Leo Ah yeah, I was too lazy to test whether the currying would work without parentheses. I need to trust more in the type inference. ;) – Martin Ender Jun 28 '17 at 9:10

# Mathematica, 41 bytes

(t=9;While[DigitCount[#][[t]]!=1,t--];t)&


thanks @Martin Ender

here is Martin's approach on my answer

# Mathematica, 35 bytes

9//.d_/;DigitCount[#][[d]]!=1:>d-1&


## R, 45 43 bytes

function(x)max(setdiff(x,x[duplicated(x)]))

Try it online!

Takes input as a vector of integers. Finds the duplicated elements, removes them, and takes the maximum. (Returns -Inf with a warning if there is no unique maximum.)

Edited into an anonymous function per comment

• max(x[!duplicated(x)]) is quite a bit shorter, but this is a great answer. I knew the way I was going to do it was not this good. Also you can remove the f= from the beginning, as anonymous functions are perfectly valid answers. Also, you can use TIO to test your functions if you use this format: Try it online! – Giuseppe Jun 28 '17 at 19:06
• Thanks! I think the 'duplicated' function doesn't count the first occurrence of a duplicate element so your version wouldn't quite work – aPaulT Jun 28 '17 at 19:10
• ah, good point. I almost never use duplicated but I actually thought up another, shorter answer! – Giuseppe Jun 28 '17 at 19:25

# Ruby, 42 bytes

->x{(?0..?9).select{|r|x.count(r)==1}[-1]}


Try it online!

• Ruby ties Python :) – Mr. Xcoder Jun 28 '17 at 8:56
• Because 42 is always the answer. :-) – G B Jun 28 '17 at 8:56
• @GB Or is it: ->x{x.chars.select{|r|x.count(r)<2}.max} – Martin Ender Jun 28 '17 at 9:00
• That would be 2 bytes shorter and ruin the whole thing. :-) – G B Jun 29 '17 at 9:02

# APL (Dyalog Unicode), 10 chars = 19 bytes

Method: multiply elements that occur multiple times by zero, and then fine the highest element.

⌈/×∘(1=≢)⌸


⌸ for each unique element and its indices in the argument:

× multiply the unique element

∘() with:

1= the Boolean for whether one is equal to

≢ the tally of indices (how many times the unique element occurs)

⌈/ the max of that

Try it online!

# APL (Dyalog Classic), 15 bytes

⌈/×∘(1=≢)⎕U2338


Try it online!

Identical to the above, but uses ⎕U2338 instead of ⌸.

# Bash + coreutils, 30 28 bytes

-2 bytes thanks to Digital Trauma

fold -1|sort|uniq -u|tail -1


Try it online!

### Bash + coreutils, 20 bytes

sort|uniq -u|tail -1


Try it online!

If input is given as a list of digits, one per line, we can skip the fold stage. That feels like cheating though.

• Replace grep -o . with fold -1 to save 2 bytes. I agree that an input integer given as a list of digits is stretching the rules too far. – Digital Trauma Jun 28 '17 at 18:54
• +1 just because it is bash – user9207 May 19 '19 at 18:39

# Python 2, 39 bytes

lambda l:max(1/l.count(n)*n for n in l)


Try it online!

• I enjoyed this, it’s great! – user9207 May 19 '19 at 4:46

# C# (.NET Core), 2797865857 75 bytes

using System.Linq;

n=>n.GroupBy(i=>i).Where(i=>i.Count()<2).Max(i=>i.Key)-48


Try it online!

Thanks @CarlosAlejo

• This does not work with "1948710498" as input (returns "9" instead of "7"), and you must add using System.Linq; to the byte count. – Charlie Jun 28 '17 at 9:03
• @CarlosAlejo Oops! Sorry! Just now read the specifications fully. Will edit the solution soon. – kakkarot Jun 28 '17 at 9:05
• Edited. Are there any optimisations I can make? – kakkarot Jun 28 '17 at 9:34
• Sure: try using OrderBy(...).Last() instead of .OrderByDescending(...).First(), for instance. Or even better, change your last part with .Max(i=>i.Key) after the Where clause. – Charlie Jun 28 '17 at 9:39
• @CarlosAlejo Thanks! Edited. – kakkarot Jun 28 '17 at 9:41

## JavaScript (ES6), 52 50 bytes

Takes input as a list of digits. Returns 0 if there are no unique digits.

s=>s.reduce((m,c)=>m>c|s.filter(x=>x==c)?m:c,0)


### Test cases

let f =

s=>s.reduce((m,c)=>m>c|s.filter(x=>x==c)?m:c,0)

console.log(f([1,2]))                 // 2
console.log(f())                   // 0
console.log(f([4,8,5,9,0,2]))         // 9
console.log(f([4,9,5,9,0,2]))         // 5
console.log(f([9,9,9,9,9,9]))         // (0)
console.log(f([9,9,9,0,9,9]))         // 0
console.log(f([1,9,4,8,7,1,0,4,9,8])) // 7

# Japt, 1211 10 bytes

Takes input as an array of digits.

k@¬èX ÉÃrw


Test it

## Explanation

     :Implicit input of array U.
k    :Filter the array to the elements that return false when...
@    :Passed through a function that...
¬    :Joins U to a string and...
èX   :Counts the number of times the current element (X) appears in the string...
É    :Minus 1.
:(The count of unique digits will be 1, 1-1=0, 0=false)
Ã    :End function.
r    :Reduce by...
w    :Getting the greater of the current element and the current value.
:Implicit output of resulting single digit integer.


# Java (OpenJDK 8), 8985 79 bytes

a->{int i=10,x[]=new int[i];for(int d:a)x[d]++;for(;i-->0&&x[i]!=1;);return i;}


Try it online!

-6 bytes thanks to @KevinCruijssen's insight!

• You can replace return i>0?i:0; with return i;. The output will be -1 for test case [9,9,9,9,9,9], but that is fine with the challenge: "If there are no unique digits, your program can do anything (undefined behavior).". – Kevin Cruijssen Jun 28 '17 at 13:43
• Indeed, I can since the current revision. Before I couldn't because of the test case 0. It's something I oversaw in the previous golf! :) – Olivier Grégoire Jun 28 '17 at 13:45

# APL (Dyalog), 14 bytes

-2 thanks toTwiNight.

⌈/⊢×1=(+/∘.=⍨)


⌈/ the largest of

⊢ the arguments

× multiplied by

1=() the Boolean for each where one equals

+/ the row sums of

∘.=⍨ their equality table

Try it online!

• Since 0 is never the highest unique digit except for 0 itself, you can save 1 byte using × instead of /⍨, then save another byte converting that into a train – TwiNight Jun 29 '17 at 1:38
• @TwiNight Nice! Thank you. – Adám Jun 29 '17 at 6:27

<?=array_flip(count_chars($argn))-48;  Try it online! # PHP, 42 bytes <?=chr(array_flip(count_chars($argn)));


Try it online!

• -2 bytes: <?=array_flip(count_chars($argn))-48; – Titus Jul 15 '17 at 8:40 # Java (JDK), 67 bytes s->{int i=9;for(s=" "+s+" ";s.split(i+"").length!=2;i--);return i;}  Try it online! # Mathematica, 42 bytes Max@Position[RotateRight@DigitCount@#,1]-1&  # F#, 88 bytes let f i=Seq.countBy(fun a->a)i|>Seq.maxBy(fun a->if snd a>1 then 0 else int(fst a))|>fst  Try it online! An improved approach from my first effort, results in less bytes. Points of interest: fst and snd return the first and second elements of a tuple respectively. # Jelly, 9 bytes ṢŒrṪỊ$ÐfṀ


Try it online!

• well – Leaky Nun Jun 28 '17 at 9:42
• @LeakyNun outgolfed, son – Skidsdev Jun 28 '17 at 9:43
• @Mayube but the core algorithm is the same – Leaky Nun Jun 28 '17 at 9:44
• @LeakyNun no, it's quite different. – steenbergh Jun 28 '17 at 9:49
• @LeakyNun I decided to post separately...basically a big difference is that in my case I just decide which to keep, while steenbergh takes some heads or something... – Erik the Outgolfer Jun 28 '17 at 9:50

# Pyth, 6 bytes

eS.m/Q


Test suite

Explanation:

eS.m/Q
eS.m/QbQ    Implicit variable introduction
.m   Q    Find all minimal elements of the input by the following function:
/Qb     Number of appearances in the input
eS          Take the maximum element remaining.


# Perl 5, 59 bytes

for$x(split//,<>){$d[$x]++};for($x=11;--$d[--$x];){}print\$x


Try it online!

• Shortened to 40 bytes: Try it online!. (you can look up -F` flag on perlrun if needed) – Dada Jul 27 '17 at 11:51