#!/usr/bin/perl
#THIS IS FILE PAR_DP.PL
# implements the DP for paragraphing
# for usage see the comments under 'usage options' below
# (at the start of the main routine)
#
use warnings;

sub c {
    my ($i,$j) = @_;
# returns cost(i,j)
    return ($j-$i) + $r*rand;
# we don't have to store the value c(i,j) since the
# routine asks for c(i,j) just once for a given
# i & j
} 

sub make_m {
# fills in the dynamic programming tables
# m, and the minimizer table k
    @m=();
    @k=();
    $m[$n+1]=0;

    for ($i=$n; $i>=1; $i--) {
	$m[$i]=$max_c;
	for ($j=$i; $j<=$n; $j++) {
	    $t=c($i,$j) + $m[$j+1];
	    if ($t<$m[$i]) {
		$m[$i]=$t; $k[$i]=$j}
	}
    }
}

sub breaks {
# prints the optimum line breaks
# calling breaks with j=0 gives the line breaks for the given problem
# calling breaks with j=s-1 gives the line breaks assuming the problem
# is given by words w(s), w(s+1),...,w(n)
    while ($j<$n ) {
	$j=$k[$j+1];
	print "$j ";
    }
    print "\n";
}

sub k_and_breaks {
# prints k array, with the optimum line breaks starred
    for $i (1..$n) {
	print "$i\t";
    }
    print "\n";
    $start=1; # start gives the beginning of the current line
    for $i (1..$n) {
        if ($i!=$start) {print "$k[$i]\t"}
        else {
	    print "$k[$i]*\t"; # k[start] is the next line break, star it
	    # unless ($next_break = $n) {$start=$k[$i]+1}; 
	    # "unless" statement is the opposite of "if": it executes the block unless the condition is true
	    $start=$k[$i]+1; # next start is right after the next line break 
	}
    } 
    print "\n";
}

$n=8;$r=3; #r=3 seems to give most variety in line breaks
$first_time=1;
while (1) {
    if ($first_time) {$opt = "f"; $first_time=0;}
    else {#do the following on every iteration except the first:
          print "[n], [r], [a]gain, [s]tart, [m] table, [k] table or [q]uit?";
# usage options:
# n  redefines n, eg, "n 12" sets n to 12 (n is the number of words)
#    dont forget to enter the number after n!
# r  redefines r, eg, "r 5" sets r to 5   (r is the coefficient in the cost function)
# a  generates a new random cost function and resolves the problem
#    keeping n & r unchanged
# s  prints the optimum breakpoints if we start with word w(s) instead of w(1)
#    eg, "s 3" prints breakpoints if input starts with word 3
#    the cost function doesn't change
# m  prints the entire DP table for the current problem
# k  prints the k array, with stars next to the entries that specify the optimum breakpoints
#  
          $in=<>;chop $in;
          ($opt, $val)=split " ",$in;
          }

    if ($opt =~ /[fnra]/) {
	if ($opt eq "n") {$n=$val} elsif ($opt eq "r") {$r=$val};
	unless ($opt eq "a") {
	    print "n= $n, c(i,j)= (j-i) + $r(rand)\n";
	    print "line breaks for words 1..$n:\n";
	    $max_c= c(1,$n)+$r+1;
	}
	make_m;
	$j=0;
	breaks;
    }
    elsif ($in eq "q") {exit}
    elsif ($in eq "m") {
	print "i ";
	for $i (1..$n) {
	    print "$i\t";
	}
	print "\n";
	print "m ";
	for $i (1..$n) {
	    printf "%3.2f\t", $m[$i];
	}
	print "\n";
	print "k ";
	for $i (1..$n) {
	    print "$k[$i]\t";
	}
	print "\n";
    }
    elsif ($in eq "k") {
	k_and_breaks;
    }    
    elsif ($opt eq "s") {
	$s=$val; 
	$j=$s-1; 
	breaks;
    }
}