title: Project Euler #11 java. Not getting the right answer
body: <p>I have some problems with <a href="https://projecteuler.net/problem=11" rel="nofollow">Problem 11</a> on Project Euler.
  I manage to get an answer, but it's not the right one. I'm getting <code>51267216</code>.
  This is found by the <code>greatestVert</code> method. I think the problem is located in the <code>greatestDiaglonal</code> method, but I'm not quite sure. Can somebody check if my algorithm is correct?</p>
  
  <p>The task is to find out what the greatest product of four adjacent numbers in any direction (up, down, left, right, or diagonally) is in the 20x20 grid.</p>
  
  <pre><code>package euler;
  
  public class Problem11 {
  
  int num1, num2, num3, num4;
  int highestNum1, highestNum2, highestNum3, highestNum4;
  
  private int sum = 0;
  
  String[] l = {
  "08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08",
  "49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00",
  "81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65",
  "52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91",
  "22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80",
  "24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50",
  "32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70",
  "67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21",
  "24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72",
  "21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95",
  "78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92",
  "16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57",
  "86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58",
  "19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40",
  "04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66",
  "88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69",
  "04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36",
  "20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16",
  "20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54",
  "01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48"
  };
  
  int greatestSide() {
      for(int i = 0;i&lt;=19;i++) {
          for(int n = 0;n&lt;=l[i].length()-12;n+=3) {
              num1 = Integer.parseInt(l[i].substring(0+n,3+n).trim());
              num2 = Integer.parseInt(l[i].substring(3+n,6+n).trim());
              num3 = Integer.parseInt(l[i].substring(6+n,9+n).trim());
              num4 = Integer.parseInt(l[i].substring(9+n,12+n).trim());
  
              if(num1*num2*num3*num4 &gt; sum) {
                  sum = num1*num2*num3*num4;
                  highestNum1 = num1;
                  highestNum2 = num2;
                  highestNum3 = num3;
                  highestNum4 = num4;
              }   
          }
      }
      return sum;
  }
  
  int greatestVert() {
      for(int i = 0; i&lt;=16; i++) {
          for(int n = 0; n&lt;=l[i].length()-3; n+=3) {
              num1 = Integer.parseInt(l[i].substring(0+n,3+n).trim());
              num2 = Integer.parseInt(l[i+1].substring(0+n,3+n).trim());
              num3 = Integer.parseInt(l[i+2].substring(0+n,3+n).trim());
              num4 = Integer.parseInt(l[i+3].substring(0+n,3+n).trim());
  
              if(num1*num2*num3*num4 &gt; sum) {
                  sum = num1*num2*num3*num4;
                  highestNum1 = num1;
                  highestNum2 = num2;
                  highestNum3 = num3;
                  highestNum4 = num4;
              }   
          }
      }
      return sum;
  }
  
  int greatestDiagonal() {
      for(int i = 19; i&gt;=3; i--) {
          for(int n = 0; n&lt;=l[i].length()-12; n+=3) {
              num4 = Integer.parseInt(l[i].substring(9+n,12+n).trim());
              num3 = Integer.parseInt(l[i-1].substring(6+n,9+n).trim());
              num2 = Integer.parseInt(l[i-2].substring(3+n,6+n).trim());
              num1 = Integer.parseInt(l[i-3].substring(0+n,3+n).trim());
  
              if(num1*num2*num3*num4 &gt; sum) {
                  sum = num1*num2*num3*num4;
                  highestNum1 = num1;
                  highestNum2 = num2;
                  highestNum3 = num3;
                  highestNum4 = num4;
              }   
          }
      }
  
      for(int i = 0; i&gt;=16; i++) {
          for(int n = 0; n&lt;=l[i].length()-12; n+=3) {
              num4 = Integer.parseInt(l[i].substring(9+n,12+n).trim());
              num3 = Integer.parseInt(l[i+1].substring(6+n,9+n).trim());
              num2 = Integer.parseInt(l[i+2].substring(3+n,6+n).trim());
              num1 = Integer.parseInt(l[i+3].substring(0+n,3+n).trim());
  
              if(num1*num2*num3*num4 &gt; sum) {
                  sum = num1*num2*num3*num4;
                  highestNum1 = num1;
                  highestNum2 = num2;
                  highestNum3 = num3;
                  highestNum4 = num4;
              }   
          }
      }
      return sum;
  }
  
  public static void main(String[] args) {
      Problem11 prog = new Problem11();
  
      prog.greatestSide();
      prog.greatestVert();
      prog.greatestDiagonal();
      System.out.println(prog.sum);
      System.out.println(prog.highestNum1);
      System.out.println(prog.highestNum2);
      System.out.println(prog.highestNum3);
      System.out.println(prog.highestNum4);
  }
  }
  </code></pre>