mission3.pl

#! /usr/bin/perl
#2014/12/09 尺取り虫とか累積和とかよーわからんのじゃー
#2014/12/13 累積和 version by Omas
 
use strict;
use warnings;
  
my @info = split(/ /,<STDIN>);
my @line = <STDIN>;
my @cum_sum = &cumsum(@line[0..$info[1] - 1]);
print(&secmax(\@cum_sum,\@info));

sub cumsum {
	my @cumsum;
	my $sum = 0;
	push(@cumsum,$sum += $_) for @_;
	return @cumsum;
} 

sub secmax {
	my ($cumsum,$info) = @_;
	my ($seclen,$len) = ($$info[0],$$info[1]);
	my ($head,$tail) = (0,$seclen);
	my ($secsum,$secmax) = (0,$$cumsum[$tail - 1]);
	while($tail < $len) {
		$secsum = $$cumsum[$tail++] - $$cumsum[$head++];
		$secmax = $secsum if $secsum > $secmax;		
	}
	return $secmax;
}