Project Euler, Problem 8: Largest Product in a Thousand Digit Series

The four adjacent digits in the 1000-digit number that have the greatest product are 9 X 9 X 8 X 9 = 5832.

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

Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

Here's the code I used to get the answer: 


$(document).ready( function() {

        // JS sucks at dealing with big numbers, but it can deal with strings pretty
        // well.  We'll have to let bignum be a string rather than an integer.
        var bignum = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";

        // Get the bignumber into an array
        var bigarr = ('' + bignum).split('').map(function(digit) {return +digit;});
        var length = bignum.length;


	// Store the products of the slices
	var bigprod = 0;

	//How deep into the bignumber do we go?
	var depth = (bigarr.length - 13);

        // Find the product of an array elements
        function multip(array) {
          prod = 1;
	  for (var i = 0; i < array.length; i++) {
	    prod = prod * array[i];
	  }
	  return prod;
	}

        // Process the 1000 digit series
	function sliceNum(bigarr) {
	  for (var n = 0; n <= depth; n++) {
	    var arslice = bigarr.slice(n,n+13);

	    var prod = multip(arslice);

	    if (prod > bigprod) { 
	      bigprod = prod; 
	      slicestart = n;
	      var topslice = bigarr.slice(slicestart, slicestart+13);
	      topslice.push(n);   // add the start index to the end of the slice
	    }
	  }
	  return topslice;
	}


        var topSlice = sliceNum(bigarr);
	var slicestart = topSlice.pop();
	var bigprod = multip(topSlice);


	$("#output").text("Product is " + bigprod.toString() 
	+ " and the 13 consecutive digits are " 
	+ bigarr.slice(slicestart, slicestart+13)+".");

});