WCW

Solution: Project Euler Problem 8

The 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

My Solution (in Java):

```
// Author: William Clausen
//
// Date: Jan 7, 2013
//
// This program solves Problem 8 from Project Euler.

public class Problem8 {

// Datamembers to hold the number of numbers to be multiplied
// and the number itself.
public int numMult;
public String nums;

Problem8(int mult, String numbers)
{
numMult = mult;
nums = numbers;
}

// This method solves the problem.
public int solve()
{
// Integers to store the largest product seen so far and
// the most recent product.
int bigProd = 1;
int newProd = 1;

// An array to keep track of which numbers are being multiplied together.
int[] multiples = new int[numMult];

// Now, loop through the whole number (which is a string) and store the last five
// numbers seen in an array. Calculate the product of those five numbers
// and check if it's the biggest product seen so far. If the new product is the
// largest seen so far, store it.
for (int i = 0; i < nums.length(); i++) {
if (multiples[i % numMult] != 0) {
newProd /= multiples[i % numMult];
}
// Here is some safety work to make sure only numbers are being multiplied.
if (Character.isDigit(nums.charAt(i))) {
multiples[i % numMult] = Integer.parseInt(nums.substring(i, i+1));
} else {
// If a non-number is encountered, then I decided the product should be
// 0 for as long as that character would have been in the array of
// stored numbers.
for (int j = 0; j < numMult; j++) {
multiples[j] = 0;
}
}
newProd = calcProd(multiples);
if (newProd > bigProd) {
bigProd = newProd;
}
}

return bigProd;
}

// Method that calculates the product of numbers stored in an array.
public int calcProd(int[] nums)
{
int prod = 1;

for (int i = 0; i < nums.length; i++) {
if (nums[i] == 0) {
return 0;
} else {
prod *= nums[i];
}
}

return prod;
}
}

```