# Output the missing integer

You will be given a string. It will contain 9 unique integers from 0-9. You must return the missing integer. The string will look like this:

123456789
> 0

134567890
> 2

867953120
> 4

• @riker That seems to be about finding a number missing in a sequence. This seems to be about finding a digit missing from a set. Mar 27 '17 at 19:48
• @Riker I wouldn't think it's a duplicate, given that the linked challenge has a strictly incrementing sequence (of potentially multi-digit numbers), whereas here it's in arbitrary order. Mar 27 '17 at 19:50
• Hi Josh! Since no one else has mentioned it so far, I'll direct you to the Sandbox where you can post future challenge ideas and get meaningful feedback before posting to main. That would have helped iron out any details (like STDIN/STDOUT) and resolved the duplicate dilemma before you received downvotes here. Mar 27 '17 at 20:23
• It's such a shame that 9-x%9 works for any digit except 0. Maybe someone more clever than me will find a way to make it work. Mar 28 '17 at 0:45
• Several answers take an integer as function input. Is that allowed? Mar 28 '17 at 0:52

# Dash (POSIX shell with POSIX utility ), 5047 27 bytes

$((1${1%0*}-1$1?9-9$1%9:0))


Try it online!

The code above evaluates to a string of digit.

## Alternative

$((1${1#*0}-1$1?9-9$1%9:0))


## How it works

• ${1%0*}. If$1 has 0, then remove digits from right up to 0; else unchanged.
• ${1#*0}. Similar but from left. • Why 1$1 and 9$9? Numbers begining from 0 is octal; but it would be syntax error if$1 has 8 and 9. They are for workarounding.

# Pxem, Filename: 28 bytes + Content: 0 bytes = 28 bytes.

• Filename (Unprintables are escaped): \011.t.w0.i.-.+.m\001.-.c.t.a\055.-.n
• Content: empty.

Try it online! (with pxem.posixism)

XX.z
# push 9; heap=pop
.a\011.tXX.z
# while empty || pop!=0; do
.a.wXX.z
# push 48; push getchar
.a0.iXX.z
# push abs(pop-pop); if size>=2; then push pop+pop; fi
.a.-.+XX.z
# push heap; push 1; push abs(pop-pop)
.a.m\001.-XX.z
# dup; heap=pop
.a.c.tXX.z
# done
.a.aXX.z
# push 48; push abs(pop-pop); printf "%d", pop
.a\055.-.n


# CSASM v2.3, 129 bytes

func main:
lda 0
sta $1 in "" conv ~arr:char pop$a
push "0123456789"
.lbl a
push $a ldelem$1
sub
inc $1 push$1
push 9
sub
brtrue a
print
ret
end


Commented and ungolfed:

func main:
; Initialize $1 to 0 lda 0 sta$1

; Get the input, convert it to an array of <char>s, then store it in $a in "" conv ~arr:char pop$a

push "0123456789"
.lbl loop
; Get the <char> in $a at index$1
push $a ldelem$1

; Remove it from the <str> currently on the stack and push the updated <str>
sub

; Increment $1 and stop looping if$1 == 9
inc $1 push$1
push 9
sub
brtrue loop

; The string will now only contain the remaining digit.  Print it
print
ret
end


# Excel, 28 bytes

=SUM(45,-MID(A2,ROW(1:9),1))


# 05AB1E, 4 bytes

žhsм


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žhsм  # full program
м  # remove all characters of...
s   # implicit input...
м  # from...
žh    # "0123456789"
# implicit output


s can also be I or ¹ and h can be m with no change in functionality.

• The APL answer wasn't #1... Dennis' jelly answer was Jun 22 at 10:20
• oof ok guess i didn't look far enough :/ Jun 26 at 20:52

# Mascarpone, 82 53 bytes

[9876543210]$v[v'$>,<]v*'#<^v'.>1#########^0123456789


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### Explanation

[9876543210]$// push the string '[9876543210' (we can ignore the '[') v // push the current interpreter [ ]v* // define an operation (under the current interpreter) v'$>,<           // "bind a symbol from stdin to 'Pop ToS'"
'#<^    // bind this operation to '#' and install it to the environment
v'.>1              // push an interpreter that defaults to "Output ToS"
#########     // bind 9 symbols from stdin to "Pop ToS"
^    // install this interpreter to the environment
0123456789         // one of these will output ToS, the rest will only pop
// the symbols to output are on the stack from line 1


# Ruby, 25 bytes

->x{'0123456789'.tr x,''}


Not terribly competitive, I'm afraid

(['0'..'9']\\)


After realizing I could just make a list with the String "0123456789" instead of the integers [0,1,2,3,4,5,6,7,8,9], the step for converting the string to integers could be skipped.

Type is now String -> String (takes a string and returns a string with the correct number). Call like:

(['0'..'9']\\)"149263708"         -- Outputs "5"


## Previous:

([0..9]\\).map digitToInt


Uses set difference, unlike the other Haskell answer, type String -> Int

Call like

([0..9]\\).map digitToInt\$"123467890"  -- Outputs 5


# Pip, 5 bytes

5 bytes seems to be the number for all golfing languages that aren't Jelly.

,tDCa


Takes input as a command-line argument. Try it online!

### Explanation

,t     Range(10)
DC   From each element, delete all characters...
a  ...that are in 1st cmdline arg
Concatenate and print (implicit)


The result is actually a list like ["";"";"";"";4;"";"";"";"";""] (which is what you get if you put RP at the front of the code). Lists by default are concatenated together before printing, so all you will see is 4.

# C (clang), 31 bytes

f(x){return x?f(x/10)-x%10:45;}


Strictly speaking, f(x) returns the sum of the missing digits. This lets me knock off a digit, get the sum of the missing digits, then add it back on.

Try it online!

# Octave, 2019 14 bytes

@(a)477-a*~~a'


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Developed independently but the same as some other answers.

a'          transpose of array a
~~a'        convert all elements of a' to 1
a*~~a'      matrix multiplication of a with a column vector of 1s
that is equivalent to sum(a)
477-a*~~a'  subtract from [477=sum('0123456789')-48]


# Java 7, 61 54 bytes

long d(int n){return(15-Long.valueOf(n+"",16)%15)%15;}


Based on @Neil's JavaScript (ES6) answer (just like JavaScript, Java uses remainder for negative-modulo. Original port is from @xnor's Python answer)

String c(int n){return"0123456789".replaceAll("["+n+"]","");}


Try it here.

## REXX, 36 bytes

#=0123456789
arg n
say verify(#,n)-1


# AHK, 39 bytes

i=[%1%]
Send % RegExReplace(99066**2,i)


Again, the inherent confusion between the input variable 1 and the actual number 1 causes confusion in AHK functions. At least it only cost 3 bytes this time.

99066**2 = 99066^2 = 9814072356 (a trick I copied from Rod's answer)

# Chip, 64 bytes

Azv~a
##'Bzv~b
^v##'Czv~c
*f|^-##'Dzv~d
Z~'~e ^-##'
ZZZZZZZ~S


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Chip is a 2D language that operates on individual bits in a byte stream. Each byte of input is broken down into its component bits for computation, then stitched back together for output.

This solution uses a rather simple algorithm, that is only a minor twist on that used by many of the other solutions:

1. Start with a value of 0x2:

 0+1+2+3+4+5+6+7+8+9 =  45 (0x2D)
~45 = -46 (0xD2)    *
-46 & 0x0F =   2  (0x2)


* I only do half of two's complement negation; I skip the increment at the end for a reason. I'll get back to this.

2. Add each code point in the string, masked with 0x0F, ignoring carries.

3. After the ninth addition, the current value will be equal to -1 minus the missing digit, masked with 0x0F:

Let's say we were missing the digit '4':

              -1 - 4 =  -5  (0xB)
~(-5) =   4  (0x4)    *


* Again, we only do half of negation. This instance cancels out the offset introduced by the previous negation.

4. Prefix the value with 0x3, giving the codepoint for the missing digit:

          0x30 | 0x4 =  52 (0x34)


What portions of the code do each bit? Well, they're a bit mixed together, but I'll try to cover the highlights:

• The # elements do the addition described in step 2.
• The z elements near the adders carry over the current value to the next cycle so that we can have a running sum.
• The Z elements keep track of which digit of the input we are on, handling the condition in step 3. They also provide the signal used to initialize the adders to 0x2, as described in step 1.
• The S element suppresses all output until the Z elements disable it on the final digit. (If you are looking at the TIO, try deleting this element to see all the intermediate values. Also, adding the flag -v will print the actual code points to stderr.)
• The letters A through D are reading the 4 low bits of the input, and a through d write those same bits of the output.
• The letters e and f provide the value 0x30 to the output as described in step 4.

# D, 24 bytes

writeln(477-readln.sum);


Just add up all characters in the given string (not terminated by a newline). The sum is s = 48 * 9 + (0 + 1 + 2 + ... + 9 - x) = 477 - x, therefore, x = 477 - s.

The calls make use of optional parentheses (-4 bytes), and .sum invocation uses uniform function call syntax (-1 more byte).

Try it online!

## Q, 24 bytes

{1#iasc"0123456789"in x}


Gets a boolean vector between the expectation and input, then sorts the indices of the expectation by that boolean vector in ascending order, first value always being the missing element since boolean for it is set to 0 and we know that value=index in this case.

## Racket 106 bytes:

(filter-not(λ(x)(member x(string->list(number->string n))))
(for/list((i(range 48 58)))(integer->char i)))


Ungolfed:

(define (f n)
(filter-not
(λ(x)
(member x
(string->list
(number->string n))))
(for/list((i(range 48 58)))(integer->char i))))


Testing:

(f 867953120)


Output:

'(#\4)


# C#, 21 bytes

z=>45-z.Sum(v=>v-'0')


The expression v-'0' takes the char value such as '3' and subtracts the char value for '0', leaving the value 3, essentially converting the character 3 into the integer 3.

45 is the sum of all the numbers 0 through 9. 45 - the sum of the passed-in integers yields the missing integer.

Sample code

public static void Main()
{
Func<string, int> X = z=>45-z.Sum(v=>v-'0');

Console.WriteLine(X("123456789"));
Console.WriteLine(X("134567890"));
Console.WriteLine(X("867953120"));
}


Test Here: https://dotnetfiddle.net/yanR5S

# Noodel, 8 bytes

ɲdFḶṡạĖ⁻


Try it:)

## How it works

ɲdFḶṡạĖ⁻
# Input implicitly pushed onto the stack.
ɲd       # Pushes the string "0123456789" onto the stack.

FḶṡạĖ⁻ # Loops nine times removing digits from the string "0123456789" producing the missing number.
F      # Pushes the string "F" onto the stack.
Ḷ     # Consumes the string "F" and converts to a base 98 number producing 9 then loops the following that many times.
ṡ    # Swaps the string "0123456789" with the input on the stack.
ạ   # Gets the ith element from the input and pushes it onto the top of the stack.
Ė  # Grabs the string "0123456789" at the bottom of the stack and puts it at the top.
⁻ # Removes the element pulled out of the input from the string.
# Implicit end of the loop.

# Implicit push to the screen, outputting the missing digit.
`