Project Euler

Problem 8: Largest Product in a Series

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

7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450

The Catch

How to calculate the product x of every 5 digits in this 1,000-digit number. For every x calculated, check if it is the maximum value obtained.

The Light

Parse the 1,000-digit number to a character array and manipulate each character. Keep track of the greatest x.

The Code

public class Problem8
{
  public static void main(String[] args)
  {
    String digit =  "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
    System.out.println(fiveDigitSum(digit));	
  }

  public static int fiveDigitSum(String s)
  {
    int max = 0;
    int tmp = 0;
    char[] digit = new char[s.length()];
    digit = s.toCharArray();

    for(int i = 0; i < digit.length - 4; i++)     
    {       
      int d1 = Character.getNumericValue(digit[i]);       
      int d2 = Character.getNumericValue(digit[i + 1]);       
      int d3 = Character.getNumericValue(digit[i + 2]);       
      int d4 = Character.getNumericValue(digit[i + 3]);       
      int d5 = Character.getNumericValue(digit[i + 4]); 	         

      tmp = d1 * d2 * d3 * d4 * d5; 	         

      if(tmp > max)
        max = tmp;
    }
    return max;	
  }
}