Project Euler, Problem #11, C

/* The task: find four adjacent numbers with the maximum product. The
 * numbers should form a line: horizontal, vertical, or diagonal.
 * Calculate the product. */

#include <stdio.h>

int main()
{
     /* matrix */
     int m[20][20] = {
          {8,  2,  22, 97, 38, 15, 0,  40, 0,  75, 4,  5,  7,  78, 52, 12, 50, 77, 91, 8},
          {49, 49, 99, 40, 17, 81, 18, 57, 60, 87, 17, 40, 98, 43, 69, 48, 4,  56, 62, 0},
          {81, 49, 31, 73, 55, 79, 14, 29, 93, 71, 40, 67, 53, 88, 30, 3,  49, 13, 36, 65},
          {52, 70, 95, 23,  4, 60, 11, 42, 69, 24, 68, 56, 1,  32, 56, 71, 37, 2,  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, 3,  45, 2,  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, 2,  62, 12, 20, 95, 63, 94, 39, 63, 8,  40, 91, 66, 49, 94, 21},
          {24, 55, 58, 5,  66, 73, 99, 26, 97, 17, 78, 78, 96, 83, 14, 88, 34, 89, 63, 72},
          {21, 36, 23, 9,  75, 0,  76, 44, 20, 45, 35, 14, 0,  61, 33, 97, 34, 31, 33, 95},
          {78, 17, 53, 28, 22, 75, 31, 67, 15, 94, 3,  80, 4,  62, 16, 14, 9,  53, 56, 92},
          {16, 39, 5,  42, 96, 35, 31, 47, 55, 58, 88, 24, 0,  17, 54, 24, 36, 29, 85, 57},
          {86, 56, 0,  48, 35, 71, 89, 7,  5,  44, 44, 37, 44, 60, 21, 58, 51, 54, 17, 58},
          {19, 80, 81, 68, 5,  94, 47, 69, 28, 73, 92, 13, 86, 52, 17, 77, 4,  89, 55, 40},
          {4,  52, 8,  83, 97, 35, 99, 16, 7,  97, 57, 32, 16, 26, 26, 79, 33, 27, 98, 66},
          {88, 36, 68, 87, 57, 62, 20, 72, 3,  46, 33, 67, 46, 55, 12, 32, 63, 93, 53, 69},
          {4,  42, 16, 73, 38, 25, 39, 11, 24, 94, 72, 18, 8,  46, 29, 32, 40, 62, 76, 36},
          {20, 69, 36, 41, 72, 30, 23, 88, 34, 62, 99, 69, 82, 67, 59, 85, 74, 4,  36, 16},
          {20, 73, 35, 29, 78, 31, 90, 1,  74, 31, 49, 71, 48, 86, 81, 16, 23, 57, 5,  54},
          {1,  70, 54, 71, 83, 51, 54, 69, 16, 92, 33, 48, 61, 43, 52, 1,  89, 19, 67, 48},
     };

     /* maximum row index */
     int mri[] = {20, 17, 17, 17};
     /* maximum column index */
     int mci[] = {17, 20, 17, 17};
     /* set type (horizontal, vertical, diagonal x 2), row, column, current product */
     int st, r, c, cp;
     /* maximum product */
     int mp = 1;

     for(st = 0; st < 4; st++)
          for(r = 0; r < mri[st]; r++)
               for(c = 0; c < mci[st]; c++)
               {
                    if(st == 0)
                         cp = m[r][c] * m[r][c + 1] * m[r][c + 2] * m[r][c + 3];
                    if(st == 1)
                         cp = m[r][c] * m[r + 1][c] * m[r + 2][c] * m[r + 3][c];
                    if(st == 2)
                         cp = m[r][c] * m[r + 1][c + 1] * m[r + 2][c + 2] * m[r + 3][c + 3];
                    if(st == 3)
                         cp = m[r][c + 3] * m[r + 1][c + 2] * m[r + 2][c + 1] * m[r + 3][c];
                    if(mp < cp)
                         mp = cp;
               }
     printf("%d", mp);
     return(0);
}

/* 70600674
 * real 0m0,002s
 * user 0m0,002s
 * sys  0m0,000s */