String with 1000 digits, find the biggest 5 digits without an array using the substring method

Question

I know my code can be made simpler and more efficient but I am trying to get it to work this way.

I want to get the biggest number consisting of 5 digits from the string. I would like to use the subString method. As output, I just get the first 5 numbers, and it doesn't loop through the rest of the string.

public class thousandDigits
{
   public static void main(String[] args)
   {

    String num = new String ("73167176531330624919225119674426574742355349194934" +
                             "96983520312774506326239578318016984801869478851843" +
                             "85861560789112949495459501737958331952853208805511" +
                             "12540698747158523863050715693290963295227443043557" +
                             "66896648950445244523161731856403098711121722383113" +
                             "62229893423380308135336276614282806444486645238749" +
                             "30358907296290491560440772390713810515859307960866" +
                             "70172427121883998797908792274921901699720888093776" +
                             "65727333001053367881220235421809751254540594752243" +
                             "52584907711670556013604839586446706324415722155397" +
                             "53697817977846174064955149290862569321978468622482" +
                             "83972241375657056057490261407972968652414535100474" +
                             "82166370484403199890008895243450658541227588666881" +
                             "16427171479924442928230863465674813919123162824586" +
                             "17866458359124566529476545682848912883142607690042" +
                             "24219022671055626321111109370544217506941658960408" +
                             "07198403850962455444362981230987879927244284909188" +
                             "84580156166097919133875499200524063689912560717606" +
                             "05886116467109405077541002256983155200055935729725" +
                             "71636269561882670428252483600823257530420752963450") ;


    int greatest = 0;
    int max = -1;
    int numChar = Integer.parseInt(num.substring(0, 5));

    for (int i = 0; i < num.length() - 5; i++) 
        {
             greatest = numChar;  

             if (max < greatest)
                {
                   max = greatest;
                }
        }
        System.out.print(max);
    }
}

The output is 7316 but it should be 99890 as the biggest 5 digit number that comes up.

Answer 1

That's because you do not update the numChar inside the loop. You only do it once at the beginning. Also, the calculated substring needs to go from i to i+5 in the loop.

int greatest = 0;
int max = -1;
//int numChar = Integer.parseInt(num.substring(0, 5)); <-- Not Here

for (int i = 0; i < num.length() - 5; i++) {
    int numChar = Integer.parseInt(num.substring(i, i + 5)); //  <-- but here
    greatest = numChar;

    if (max < greatest) {
        max = greatest;
    }
}