aoc

aoc_2024_4_1.c (1413B)

---

 #include <stdbool.h>
 #include <string.h>
 
 #define NELEMS(x) (int) (sizeof(x) / sizeof((x)[0]))
 #define MATCH "XMAS"
 
 typedef struct {
   int y;
   int x;
 } dir_t;
 
 const dir_t DIRS[8] = {
   {  1,  0 },
   { -1,  0 },
   {  0,  1 },
   {  0, -1 },
   {  1,  1 },
   {  1, -1 },
   { -1,  1 },
   { -1, -1 },
 };
 
 long perform(char *data) {
   int len = strlen(data);
   int rows = 0;
   int cols = 0;
   for (int i = 0; i < len; i++) {
     char c = data[i];
     if (c == '\n') {
       if (rows == 0) {
         cols = i;
       }
       rows++;
     }
   }
   char grid[rows][cols];
   for (int i = 0; i < len; i++) {
     char c = data[i];
     if (c == '\n') {
       continue;
     }
     int y = i / (cols + 1);
     int x = i % (cols + 1);
     grid[y][x] = data[i];
   }
   int count = 0;
   for (int y = 0; y < rows; y++) {
     for (int x = 0; x < cols; x++) {
       for (int i = 0; i < NELEMS(DIRS); i++) {
         dir_t dir = DIRS[i];
         bool is_match = true;
         for (int j = 0; j < (int) strlen(MATCH); j++) {
           int ry = y + j * dir.y;
           int rx = x + j * dir.x;
           if (ry < 0 || ry >= rows || rx < 0 || rx >= cols) {
             is_match = false;
             break;
           }
           char c = grid[ry][rx];
           if (c != MATCH[j]) {
             is_match = false;
             break;
           }
         }
         if (is_match) {
           count++;
         }
       }
     }
   }
   return count;
 }