#!/usr/bin/perl
use Modern::Perl;

my $count =  1;         # track the next one to do
my $end   = 10;         # set to 3_000_050 for real run

open my $infile, '<', '937753-input.txt' or die $!;
while(<$infile>){
    if( /(\d+)\s+(\d+)/ ){           # extract two numbers
        my($k, $v) = ($1, $2);       # and put them in named variables
        if ( $k > $count ) {         # see if we skipped any
            for my $n ($count..($k-1)) {
                say "$n\t0";         # and ouput them with 0 if we did
            }
        }
        say "$k\t$v";             # then output the current one
        $count = $k + 1;          # and reset the counter
    }
}

if ( $count < $end ) {        # are any numbers missing at the end?
    for my $n ($count .. $end) {
        say "$n\t0";              # output them with zeros
    }
}
__END__

# 937753-input.txt
3   5
4   7
6   7
7   0
8   8

# tab-separated output
1       0
2       0
3       5
4       7
5       0
6       7
7       0
8       8
9       0
10      0