1 files changed, 156 insertions, 0 deletions

diff --git a/2023/10/10b.c b/2023/10/10b.c
new file mode 100644
index 0000000..0b298dc
--- /dev/null
+++ b/2023/10/10b.c
@@ -0,0 +1,156 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define N 1000
+#define set(i, j, c) if (newmap[i][j] == '.') newmap[i][j] = c;
+
+typedef enum { EAST, SOUTH, WEST, NORTH } direction_t;
+
+char map[N+2][N+2], newmap[N+2][N+2];
+int n, si, sj, count[26] = {0};
+direction_t sdir;
+
+void printmap(char m[][N+2]) {
+        for (int i = 1; i < n; i++) {
+                for (int j = 1; m[i][j] != 'B'; j++)
+                        printf("%c", m[i][j]);
+                printf("\n");
+        }
+}
+
+void color_rl(direction_t dir, int i, int j) {
+        switch (dir) {
+        case EAST:
+                set(i-1, j, 'L');
+                set(i+1, j, 'R');
+                break;
+        case SOUTH:
+                set(i, j+1, 'L');
+                set(i, j-1, 'R');
+                break;
+        case WEST:
+                set(i-1, j, 'R');
+                set(i+1, j, 'L');
+                break;
+        case NORTH:
+                set(i, j+1, 'R');
+                set(i, j-1, 'L');
+                break;
+        default:
+                break;
+        }
+}
+
+direction_t firstdir(int i, int j) {
+        if (map[i][j+1] ==  '7' || map[i][j+1] == '-' || map[i][j+1] == 'J')
+                return EAST;
+        if (map[i+1][j] ==  'L' || map[i+1][j] == '|' || map[i+1][j] == 'J')
+                return SOUTH;
+        return WEST;
+}
+
+void advance(int *i, int *j, direction_t dir) {
+        if (dir == EAST) { (*j)++; }
+        else if (dir == SOUTH) { (*i)++; }
+        else if (dir == WEST) { (*j)--; }
+        else (*i)--;
+}
+
+direction_t newdir(int i, int j, direction_t dir) {
+        switch (map[i][j]) {
+        case '|':
+        case '-':
+                return dir;
+        case '7':
+                if (dir == EAST) return SOUTH;
+                if (dir == NORTH) return WEST;
+        case 'F':
+                if (dir == WEST) return SOUTH;
+                if (dir == NORTH) return EAST;
+        case 'J':
+                if (dir == EAST) return NORTH;
+                if (dir == SOUTH) return WEST;
+        case 'L':
+                if (dir == WEST) return NORTH;
+                if (dir == SOUTH) return EAST;
+        default:
+                printf("Error: dead path at (%d, %d)\n", i, j);
+                exit(1);
+        }
+        return EAST;
+}
+
+void walk_and_color_rl(char c) {
+        int i = si, j = sj;
+        direction_t dir = sdir;
+
+        newmap[i][j] = c;
+        color_rl(dir, i, j);
+        advance(&i, &j, dir);
+        for (; map[i][j] != 'S'; advance(&i, &j, dir)) {
+                newmap[i][j] = c;
+                color_rl(dir, i, j);
+                dir = newdir(i, j, dir);
+                color_rl(dir, i, j);
+        }
+        color_rl(dir, i, j);
+}
+
+void fill(int i, int j, char c) {
+        if (newmap[i][j] != '.' && newmap[i][j] != 'R' && newmap[i][j] != 'L')
+                return;
+
+        newmap[i][j] = c;
+        count[c-'a']++;
+        fill(i, j+1, c);
+        fill(i, j-1, c);
+        fill(i+1, j, c);
+        fill(i-1, j, c);
+}
+
+int main() {
+        /* Get input */
+        for (n = 1; fgets(&map[n][1], N, stdin) != NULL; n++) ;
+
+        /* Add borders, copy to newmap */
+        for (int i = 0; i < N+2; i++) {
+                for (int j = 0; j < N+2; j++) {
+                        newmap[i][j] = map[i][j];
+                        if (map[i][j] == 0 || map[i][j] == '\n')
+                                newmap[i][j] = map[i][j] = 'B';
+                }
+        }
+
+        /* Find S and set the initial direction */
+        for (si = 1; si < n; si++)
+                for (sj = 1; map[si][sj] != 'B'; sj++)
+                        if (map[si][sj] == 'S')
+                                goto found_s;
+
+found_s:
+        /* Set the initial direction and walk the path mark it with X */
+        sdir = firstdir(si, sj);
+        walk_and_color_rl('X');
+
+        /* Replace the unnecessary pipe symbols with dots */
+        for (int i = 1; i < N; i++)
+                for (int j = 1; map[i][j] != 'B'; j++)
+                        if (newmap[i][j] != 'X')
+                                newmap[i][j] = '.';
+
+        /* Walk again the path and mark adjacent dots left and right */
+        walk_and_color_rl('Y');
+
+        /* Mark the remaining dots left and right */
+        for (int i = 1; i < n; i++)
+                for (int j = 1; newmap[i][j] != 'B'; j++)
+                        if (newmap[i][j] == 'R' || newmap[i][j] == 'L')
+                                fill(i, j, newmap[i][j] + 'a' - 'A');
+
+        printmap(newmap);
+        printf("r: %d\nl: %d\n", count['r'-'a'], count['l'-'a']);
+        printf("Check with the map printed above which one is 'inside'\n");
+        return 0;
+}