This is my response to The Weekly Challenge #250.
@ints.
i such that
i mod 10 == $ints[i] otherwise return -1.
Input: @ints = (0, 1, 2)
Output: 0
i=0: 0 mod 10 = 0 == $ints[0].
i=1: 1 mod 10 = 1 == $ints[1].
i=2: 2 mod 10 = 2 == $ints[2].
All indices have i mod 10 == $ints[i], so we return the smallest index 0.
Input: @ints = (4, 3, 2, 1)
Output: 2
i=0: 0 mod 10 = 0 != $ints[0].
i=1: 1 mod 10 = 1 != $ints[1].
i=2: 2 mod 10 = 2 == $ints[2].
i=3: 3 mod 10 = 3 != $ints[3].
2 is the only index which has i mod 10 == $ints[i].
Input: @ints = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
Output: -1
Explanation: No index satisfies i mod 10 == $ints[i].
#! /usr/bin/env raku
unit sub MAIN (*@ints where @ints.elems > 0 && all(@ints) ~~ Int); # [1]
for ^@ints -> $i # [2]
{
if $i % 10 == @ints[$i] # [3]
{
say $i; # [3a]
exit; # [3b]
}
}
say -1; # [4]
[1] At least one element, and they must all be integers.
[2] Iterate over the array indices (from 0 and upwards).
[3] Use the modula operator % as prescribed.
If it works, print the current index and exit.
See docs.raku.org/routine/% for more information about the modulo operator %.
[4] No match. Say so.
Running it:
$ ./smallest-index 0 1 2
0
$ ./smallest-index 4 3 2 1
2
$ ./smallest-index 1 2 3 4 5 6 7 8 9 0
-1
Looking good.
No verbose mode this time.
Input: @alphanumstr = ("perl", "2", "000", "python", "r4ku")
Output: 6
"perl" consists of letters only so the value is 4.
"2" is digits only so the value is 2.
"000" is digits only so the value is 0.
"python" consits of letters so the value is 6.
"r4ku" consists of letters and digits so the value is 4.
Input: @alphanumstr = ("001", "1", "000", "0001")
Output: 1
#! /usr/bin/env raku
unit sub MAIN (*@alphanumstr where @alphanumstr.elems > 0, # [1]
:v(:$verbose));
my @values = @alphanumstr.map({ /^<[0..9]>+$/ ?? $_.Int !! $_.chars }); # [2]
say ":Values: { @values.join(",") }" if $verbose;
say @values.max; # [3]
[1] At least one element. Note the lack of alphanumeric enforcement.
[2]
Use map to map each element to a number. That number
is the value itself - coerced to an integer with Int to get rid of any
leading zeroes, if it only contains (ascii) digits, and the string length (with
chars) otherwise.
See docs.raku.org/routine/map for more information about map.
See docs.raku.org/routine/Int for more information about the Int coercer.
See docs.raku.org/routine/chars for more information about chars.
[3] Print the highest value.
Running it:
$ ./asv perl 2 000 python r4ku
6
$ ./asv 001 1 000 0001
1
Looking good.
With verbose mode:
$ ./asv -v perl 2 000 python r4ku
:Values: 4,2,0,6,4
6
$ ./asv -v 001 1 000 0001
:Values: 1,1,0,1
1
And that's it.