What is this date format?

Question

For Gregorian calendars, the date format varies from a country to another. There are three main formats recognized:

1. YY-MM-DD (big-endian)
2. DD-MM-YY (little-endian)
3. MM-DD-YY (middle-endian)

Your task is to write a program which, given an input string representing a date, output all the possible date formats by which this string can be interpreted as a date.

Rules

• The input date is in the format xx-xx-xx, where each field is two digits and zero-padded.
• The date is always valid (so you cannot get things like 14-13-17)
• The date is always at least one of the formats above (so you cannot get things like 17-14-11)
• Because we are in fact in a parallel world, there are 31 days for every month of the year, and consequently no leap years
• The date is between January 01, 2001 and December 31, 2099
• If there is only one format for the date, the code must print only it (only trailing newlines are allowed)
• If there are several formats for the date, they must be either separated by a comma, a space, a newline, or a combination of those
• You must output the exact name(s) of the format(s). Using distinct arbitrary values is not allowed.
• No leading or trailing characters others than a trailing space are allowed
• The output must be lowercase
• You are not allowed to use any built-in date or calendar functions
• The output formats do not have to be sorted

Examples

Input      Output
30-05-17   big-endian, little-endian
05-15-11   middle-endian
99-01-02   big-endian
12-11-31   big-endian, little-endian, middle-endian
02-31-33   middle-endian

This is code-golf so the shortest code in bytes wins. Explanations are encouraged.

Answer 1

Python 2, 123 bytes

a,b,c=map(int,input().split('-'))
for a,b,c in[[b,c,'big'],[b,a,'little'],[a,b,'middle']]:print(c+'-endian')*(a<13)*(b<32),

Try it online!

---

Python 2, less input parsing, 123 bytes

d=input()
for a,b,c in[[3,6,'big'],[3,0,'little'],[0,3,'middle']]:print(c+'-endian')*(int(d[a:a+2])<13)*(int(d[b:b+2])<32),

Try it online!

Answer 2

JavaScript (ES6), 121 119 118 112 bytes

Returns a space-delimited string with a trailing space.

s=>['big','little','middle'].map((v,i)=>[b<13&c<32,b<13&a<32,a<13][i]?v+'-endian ':'',[a,b,c]=s.split`-`).join``

How?

We split the input into a, b and c. Because the date is guaranteed to be valid, we know for sure that b is less than 32. Therefore, it's enough to test whether a is less than 13 to validate the middle-endian format. Little-endian and big-endian formats require b to be less than 13 and another test on a and c respectively to validate the day.

Hence the 3 tests:

• Big-endian: b < 13 & c < 32
• Little-endian: b < 13 & a < 32
• Middle-endian: a < 13

Test cases

let f =

s=>['big','little','middle'].map((v,i)=>[b<13&c<32,b<13&a<32,a<13][i]?v+'-endian ':'',[a,b,c]=s.split`-`).join``

console.log(f("30-05-17")) // big-endian, little-endian
console.log(f("05-15-11")) // middle-endian
console.log(f("99-01-02")) // big-endian
console.log(f("12-11-31")) // big-endian, little-endian, middle-endian
console.log(f("02-31-33")) // middle-endian

Answer 3

05AB1E, 40 bytes

'-¡©2£13‹`®Á2£32‹*)˜“Œ±„¥„ê“#Ï’-„–ian’«»

Try it online!

Explanation

'-¡©                                      # split on "-" and store a copy in register
    2£13‹                                 # compare the first 2 elements to 13
         `                                # split as separate to stack
                                          # the bottom element is true if it is middle endian
                                          # the top value is true if it can be big/little
          ®Á                              # retrieve the list from register and rotate right
            2£32‹                         # compare the first 2 elements to 32
                 *                        # multiply with the result of the comparison to 13
                  )˜                      # wrap in a flattened list
                    “Œ±„¥„ê“#             # push the list ['middle', 'big', 'little']
                             Ï            # index into this with the flattened list
                                          # this leaves the types the date could be
                              ’-„–ian’«   # append "-endian" to each
                                       »  # join on newlines

Answer 4

Bash, 240 125 116 112 bytes

IFS=- read a b c<<<$1
d=-endian
((b<13))&&(((a<32))&&echo little$d;((c<32))&&echo big$d);((a<13))&&echo middle$d

Golfed.

Thanks to manatwork for some tips

Saved 9 bytes removing the verification for less than 32 in the middle-endian follwing Arnauld answer

Saved 4 bytes by using different variables instead of an array

Test it!

Answer 5

C#, 180 bytes

t=(n,m)=>int.Parse(n)<13&int.Parse(m)<32;s=>{var a=s.Split('-');return$"{(t(a[1],a[2])?"big-endian":"")} {(t(a[1],a[0])?"little-endian":"")} {(t(a[0],a[1])?"middle-endian":"")}";};

Outputs with only space separated values, can also have leading and trailing spaces. Will update when the OP has clarified on that point if needed.

Full/Formatted version:

Func<string, string, bool> t = (n, m) => int.Parse(n) < 13 & int.Parse(m) < 32;

Func<string, string> f = s =>
{
    var a = s.Split('-');

    return $"{(t(a[1], a[2]) ? "big-endian" : "")} {(t(a[1], a[0]) ? "little-endian" : "")} {(t(a[0], a[1]) ? "middle-endian" : "")}";
};

Answer 6

PHP, 151 Bytes

[$a,$b,$c]=sscanf($argn,"%d-%d-%d");$z="-endian ";echo($m=$b&&$b<13)&&$c&&$c<32?big.$z:"",$m&&$a&&$a<32?little.$z:"",$a&&$a<13&&$b&&$b<32?middle.$z:"";

Testcases

Answer 7

Batch, 138 bytes

@echo off
set/ps=
call:l little %s:-= %
exit/b
:l
call:e big %4 %3
call:e middle %3 %2
:e
if %2 leq 31 if %3 leq 12 echo %1-endian

Vaguely based on @ovs's answer.

Answer 8

Java 232 bytes

(String s)=>{String[]i=s.split("-");String e="-endian",b="big"+e,m="middle"+e,l="little"+e;int p=Integer.valueOf(i[0]);System.out.print(p<13?Integer.valueOf(i[1])<13?Integer.valueOf(i[2])<32?b+","+m+","+l:m+","+l:m:p<32?b+","+l:b);}

Here's a nicer version

String[] i = s.split("-");

String e = "-endian",
       b = "big" + e,
       m = "middle" + e,
       l = "little" + e;

int p = Integer.valueOf(i[0]);

I didn't really know how to format this part...

System.out.print(
        p < 13 ? Integer.valueOf(I[1]) < 13 ? Integer.valueOf(I[2]) < 32 ? b + "," + m + "," + l
                                                                         : m + "," + l
                                            : m 

               : p < 32 ? b + "," + l 
                        : b
);

Answer 9

PHP, 131 bytes

[$a,$b,$c]=explode('-',$argn);foreach([[big,b,c],[little,b,a],[middle,a,b]]as[$t,$x,$y])echo$$x*$$y&&$$x<13&$$y<32?"$t-endian ":"";