Solution to Project Euler Problem 8 - greatest product of five consecutive digits in a 1000-digit number.

http://projecteuler.net/problem=8

Problem:

Find the greatest product of five consecutive digits in the 1000-digit number.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

Answer: The greatest product of five consecutive digits is: 40824

            i.e 9*9*8*7*9=40824

Solution: 

# Store this 1000 digit number in a file named p8-input.txt

#!/usr/bin/perl -w
use strict;
my (@number, @temp, $end, $i,$j,@sum);


open (FH, "p8-input.txt") || die "Cant open p8-input.txt $! ";


#Read input file into array, by splitting each number
foreach() {
        chomp($_);
        #Split a number into array
        @temp = ( $_ =~ m/./g ) ;
        @number=(@number, @temp );
}
#for thousand numbers, for loop should end at index 996 (index starts from 0)
$end=$#number-3;


for ($i=0;$i<$end;$i++) {
#Keep finding sum of consecutive 5 numbers and store it in an array
        $sum[$i]=$number[$i]*$number[$i+1]*$number[$i+2]*$number[$i+3]*$number[$i+4];
        print "$number[$i]*$number[$i+1]*$number[$i+2]*$number[$i+3]*$number[$i+4]=$sum[$i] \n";
}


#sort the sum array numerically
@sum=sort{ $a <=> $b } @sum;


print "The greatest product of five consecutive digits is: $sum[$#sum] \n";