http://rosalind.info/problems/spec/

Sample input

3524.8542
    3710.9335
    3841.974
    3970.0326
    4057.0646

Sample output

WMQS

use v6;



constant monoisotopic-mass-table = Hash.new: <
    A   71.03711
    C   103.00919
    D   115.02694
    E   129.04259
    F   147.06841
    G   57.02146
    H   137.05891
    I   113.08406
    K   128.09496
    L   113.08406
    M   131.04049
    N   114.04293
    P   97.05276
    Q   128.05858
    R   156.10111
    S   87.03203
    T   101.04768
    V   99.06841
    W   186.07931
    Y   163.06333
>;

my @default-data = qw:to/END/;
    3524.8542
    3710.9335
    3841.974
    3970.0326
    4057.0646
    END

sub spec(@weight, :$accuracy = .01) {
    my @a = my @b = sort *.Num, @weight;
    join '', gather
    for @b[1..*] Z- @b[0..*] -> $mass {
        take .key given
        first { abs($_.value - $mass) < $accuracy },
        monoisotopic-mass-table;
    }
}

sub MAIN($input-file = Nil) {
    my @weights = $input-file ?? $input-file.IO.lines !! @default-data;
    say spec @weights;
}

# vim: expandtab shiftwidth=4 ft=perl6