It won't produce 'optimal' results, but for display purposes it will probably be 'good enough'. It also has the virtues of being simple and determanistic (fast).

Basically, sort the segment/length pairs ascending by segment, descending by length. Scan the sorted array backward putting the next value into the current group (line) if it doesn't overlap the previous entry. When you can fit no more, start a new group (line). Repeat until no more bits:

#! perl -slw
use strict;
use Data::Dump qw[ pp ];

## Generate some data
my $string = '1234567890' x 7;
my @bits = map[ int rand length $string, 2 + int rand 10 ], 1 .. 20;

## Sort ascending offset/descending length
@bits = sort{
    $a->[ 0 ] <=> $b->[ 0 ]
    ||
    $b->[ 1 ] <=> $a->[ 1 ]
} @bits;

## build groups
my @groups;

## Till done
while( @bits ) {
    ## start a new group with the last bit
    push @groups, [  pop @bits ];

    ## Scan the rest of the bits (backward so we can splice without ba
+d kharma)
    for my $bit ( reverse 0 .. $#bits ) {
        ## if it'll fit in this line
        if( $bits[ $bit ][ 0 ]+ $bits[ $bit ][ 1 ] < $groups[-1][-1][0
+] ) {
             ## add it
            push @{ $groups[-1] }, splice @bits, $bit, 1;
        }
    }
}

## display the results
print $string;
for my $group ( @groups ){
    my $line = ' ' x 70;
    for my $bit ( @{ $group } ) {
        substr $line, $bit->[ 0 ], $bit->[ 1 ], 
            substr $string, $bit->[ 0 ], $bit->[ 1 ];
    }
    print $line;
}

__END__
c:\test>700817.pl
1234567890123456789012345678901234567890123456789012345678901234567890
 23    89    4567890    567890123     9012  567890123      012       0
           234567890    56789012345   901234567                45678
          123456789    45678    3456789012               890123
        90123456      3456789
                     234
                  90123456

c:\test>700817.pl
1234567890123456789012345678901234567890123456789012345678901234567890
           2345  890123  6789012  5678   234567  012345      2345   90
    5678901234  789012345     12345          67890123      01234    90
   45678901    6789                      234567890            34567
                                       0123456789         9012345

c:\test>700817.pl
1234567890123456789012345678901234567890123456789012345678901234567890
                    1234567     34567    234567890        9012       0
            345678901   5678901    6789012               89012  567890
                     23456789012  567890                     234567890
             4567890123   789012345                        0123456789
                        5678901234
                       45678901234
                 89012345
              56789012345

c:\test>700817.pl
1234567890123456789012345678901234567890123456789012345678901234567890
123456  90    56789012  56789     567    234567   1234       234567890
     67   123456789            23456      345678901        01234
     678901234                1234                       890
                           890123456                     89012
                         678901234                   45678901
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