Project Euler Problem 11: Largest product in a grid

Problem

In the 20×20 grid below, four numbers along a diagonal line have been marked in red.

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

The product of these numbers is 26 × 63 × 78 × 14 = 1788696.

What is the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid?

Solution

It is worth mentioning that the algorithm to calculate adjacent product for horizontal, vertical and diagonal direction can be consolidated.

      private static final int SIZE = 20;  
      private static final int[][] m = new int[SIZE][SIZE];  
      private static final int K = 4;  
      public static void main(String[] args) {  
           readFile();  
           int greatestProduct = 0;  
           for (int i=0; i<SIZE; i++){  
                for (int j=0; j<SIZE; j++){  
                     int rowProduct = adjacentProduct(i, j, 1, 0);  
                     int colProduct = adjacentProduct(i, j, 0, 1);  
                     int diagProductRight = adjacentProduct(i, j, 1, 1);  
                     int diagProductLeft = adjacentProduct(i,j, 1, -1);  
                     int tempGreatest = Math.max(Math.max(rowProduct, colProduct),   
                               Math.max(diagProductLeft, diagProductRight));  
                     greatestProduct = Math.max(greatestProduct, tempGreatest);  
                }  
           }  
           System.out.println(greatestProduct);  
      }  
      private static int adjacentProduct(int i, int j, int iStep, int jStep){  
           int iK = i+iStep*(K-1);  
           int jK = j+jStep*(K-1);  
           if (!withinBoundary(iK) || !withinBoundary(jK)){  
                return 0;  
           }  
           int product = 1;  
           for (int x=i,y=j,count=0; count<K; x+=iStep,y+=jStep, count++){  
                product *= m[x][y];  
           }  
           return product;  
      }  
      private static boolean withinBoundary(int i) {  
           return 0 <= i && i < SIZE;  
      }  
      private static void readFile() {  
           File file = new File("Q11.txt");  
           try {  
                Scanner sc = new Scanner(file);  
                int row = 0;  
                int col = 0;  
                while (sc.hasNextLine()) {  
                     int i = sc.nextInt();  
                     m[row][col] = i;  
                     col++;  
                     if (col == SIZE){  
                          col = 0;  
                          row++;  
                     }  
                }  
                sc.close();  
           } catch (FileNotFoundException e) {  
                e.printStackTrace();  
           }  
      }