Day 25 solutions. Merry Christmas!

I did not get all the stars, but it was a good challenge trying to do all the days in C only. Next year I'll give C++ or Rust a try.

25/25-1.c

@@ -0,0 +1,159 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+
+typedef enum
+{
+    EMPTY = 0,
+    EAST,
+    SOUTH,
+} DIRECTION;
+
+typedef struct
+{
+    DIRECTION current_direction;
+    DIRECTION next_direction;
+} CELL;
+
+typedef struct
+{
+    CELL **space;
+    int width;
+    int height;
+    bool modified;
+} SPACE;
+
+SPACE *new_space(int height)
+{
+    SPACE *p_space = calloc(1, sizeof(SPACE));
+    p_space->space = calloc(height, sizeof(CELL *));
+    p_space->height = height;
+    return p_space;
+}
+
+#define ITER_SPACE(space, i, j)                  \
+    for (size_t i = 0; i < (space)->height; i++) \
+        for (size_t j = 0; j < (space)->width; j++)
+
+void step_space(SPACE *space)
+{
+    space->modified = false;
+    ITER_SPACE(space, i, j)
+    {
+        if (space->space[i][j].current_direction == EAST &&
+            space->space[i][(j + 1) % space->width].current_direction == EMPTY)
+        {
+            space->space[i][(j + 1) % space->width].next_direction = EAST;
+            space->space[i][j].next_direction = EMPTY;
+            space->modified = true;
+        }
+    }
+    ITER_SPACE(space, i, j)
+    {
+        space->space[i][j].current_direction = space->space[i][j].next_direction;
+    }
+    ITER_SPACE(space, i, j)
+    {
+        if (space->space[i][j].current_direction == SOUTH &&
+            space->space[(i + 1) % space->height][j].current_direction == EMPTY)
+        {
+            space->space[(i + 1) % space->height][j].next_direction = SOUTH;
+            space->space[i][j].next_direction = EMPTY;
+            space->modified = true;
+        }
+    }
+    ITER_SPACE(space, i, j)
+    {
+        space->space[i][j].current_direction = space->space[i][j].next_direction;
+    }
+}
+
+void *print_space(SPACE *space)
+{
+    for (size_t i = 0; i < space->height; i++)
+    {
+        for (size_t j = 0; j < space->width; j++)
+        {
+            switch (space->space[i][j].current_direction)
+            {
+            case EMPTY:
+                putchar('.');
+                break;
+            case EAST:
+                putchar('>');
+                break;
+            case SOUTH:
+                putchar('v');
+                break;
+            }
+        }
+        putchar('\n');
+    }
+    putchar('\n');
+}
+
+//
+
+unsigned int get_lines(char *file)
+{
+    FILE *p_file = fopen(file, "r");
+    unsigned int lines = 0;
+    char c;
+    while ((c = getc(p_file)) != EOF)
+        if (c == '\n')
+            lines++;
+    return lines;
+}
+
+SPACE *read_space_file(char *file_name)
+{
+    int lines = get_lines(file_name);
+    SPACE *p_space = new_space(lines);
+    FILE *p_file = fopen(file_name, "r");
+    int i = 0;
+    char buf[BUFSIZ];
+    while (fgets(buf, sizeof buf, p_file) != NULL)
+    {
+        buf[strcspn(buf, "\n")] = '\0';
+        int len = strlen(buf);
+        p_space->space[i] = calloc(len, sizeof(CELL));
+        p_space->width = len;
+        for (int j = 0; j < len; j++)
+        {
+            DIRECTION direction;
+            switch (buf[j])
+            {
+            case '.':
+                direction = EMPTY;
+                break;
+            case '>':
+                direction = EAST;
+                break;
+            case 'v':
+                direction = SOUTH;
+                break;
+            }
+            p_space->space[i][j].current_direction = direction;
+            p_space->space[i][j].next_direction = direction;
+        }
+        i++;
+    }
+    return p_space;
+}
+
+int main(int argc, char const *argv[])
+{
+    SPACE *p_space = read_space_file("input");
+    int step_counter = 0;
+    do
+    {
+        step_space(p_space);
+        step_counter++;
+    } while (p_space->modified);
+
+    // print_space(p_space);
+    printf("STEP %d\n", step_counter);
+
+    return 0;
+}