#!/usr/bin/perl
use v5.40;

sub day1_1( $filename ) {
    open my $fh, '<', $filename;

    my @list1;
    my @list2;

    my $counter = 0;
    while(my $line = readline $fh) {
        my @data = split " ", $line;
        if (@data == 2) {
            push @list1, $data[0];
            push @list2, $data[1];
        } else {
            print "More than two data points found at: $counter\n";
            return -1;
        }
        $counter++;
    }

    @list1 = sort @list1;
    @list2 = sort @list2;

    if (@list1 != @list2) {
        print("indices don't match\n");
        return -1;
    }

    my $total = 0;
    foreach my $i ( 0 .. $#list1) {
        $total += abs($list1[$i] - $list2[$i]);
    }

    close $fh;

    return $total;
}

sub find_count($item, $is_sorted, @list) {
    if($is_sorted != 1) {
        @list = sort @list;
    }

    my $lower_bound = 0;
    my $upper_bound = $#list;
    my $index = 0;
    my $found_location = 0;
    until($found_location == 1) {
        if ($upper_bound - $lower_bound <= 1) {
            if ($list[$upper_bound] == $item) {
                $index = $upper_bound;
                last;
            } elsif ($list[$lower_bound] == $item) {
                $index = $lower_bound;
                last;
            } else {
                return 0;
            }
        }
        $index = round(($upper_bound + $lower_bound) / 2);
        if ($list[$index] > $item) {
            $upper_bound = $index;
        } elsif ($list[$index] < $item) {
            $lower_bound = $index;
        } else {
            last;
        }
    }

    my $count = 1;

    my $index_above = $index + 1;
    my $index_lower = $index - 1;
    my $index_above_found = 1;
    my $index_lower_found = 1;

    while( $index_above_found == 1 || $index_lower_found == 1 ) {
        if($index_above_found == 1) {
            if($list[$index_above] == $item) {
                $count++;
                $index_above++;
            } else {
                $index_above_found = 0;
            }
        }

        if($index_lower_found == 1) {
            if($list[$index_lower] == $item) {
                $count++;
                $index_lower--;
            } else {
                $index_lower_found = 0;
            }
        }
    }

    return $count;
}

sub day1_2( $filename ) {
    open( my $FH, '<', $filename) or die $!;

    my @list1;
    my @list2;

    my $counter = 0;
    while(<$FH>) {
        my @data = split(" ", $_);
        if (@data == 2) {
            push(@list1, $data[0]);
            push(@list2, $data[1]);
        } else {
            print("More than two data points found at: $counter\n");
            return -1;
        }
        $counter++;
    }

    if($#list1 != $#list2) {
        print("indices don't match\n");
        return -1;
    }

    @list1 = sort @list1;
    @list2 = sort @list2;

    my $total = 0;
    my $prev_num = 0;
    my $prev_count = 0;
    foreach my $item (@list1) {
        my $loc_count = 0;
        if ($item == $prev_num ) {
            $loc_count = $prev_count;
        } else {
            $loc_count = find_count($item, 1, @list2);
        }
            
        $total += $item * $loc_count;
        $prev_num = $item;
        $prev_count = $loc_count;
    }

    return $total;
}

my $data = "./input_day_1_1.txt";
my $sum = day1_1($data);
my $simi = day1_2($data);
print("Sum of differences: $sum\n");
print("Similarity score: $simi\n");