1 files changed, 51 insertions, 0 deletions

diff --git a/2023/16/16b.c b/2023/16/16b.c
new file mode 100644
index 0000000..ce42c31
--- /dev/null
+++ b/2023/16/16b.c
@@ -0,0 +1,51 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define M 200
+#define MAX(x,y) ((x)>(y)?(x):(y))
+
+char map[M][M];
+int s, t, n, nb, b[M][2], entered[M][M];
+
+#define E 1
+#define N 2
+#define W 4
+#define S 8
+int turn[9][255] = {
+        [E] = { ['.'] = E, ['-'] = E,   ['/'] = N, ['\\'] = S, ['|'] = N|S },
+        [N] = { ['.'] = N, ['-'] = E|W, ['/'] = E, ['\\'] = W, ['|'] = N   },
+        [W] = { ['.'] = W, ['-'] = W,   ['/'] = S, ['\\'] = N, ['|'] = N|S },
+        [S] = { ['.'] = S, ['-'] = E|W, ['/'] = W, ['\\'] = E, ['|'] = S   },
+};
+int go[9][2] = { [E] = {0, 1}, [N] = {-1, 0}, [W] = {0, -1}, [S] = {1, 0} };
+
+void walk(int i, int j, int d) {
+        if (i < 0 || j < 0 || i >= n || j >= n || (entered[i][j] & d)) return;
+        if (!entered[i][j]) s++;
+        entered[i][j] |= d;
+        for (int k = 1; k <= 8; k <<= 1)
+                if (k & turn[d][map[i][j]])
+                        walk(i+go[k][0], j+go[k][1], k);
+}
+
+void clear(void) {
+        s = 0;
+        for (int i = 0; i < n; i++)
+                memset(entered[i], 0, n * sizeof(int));
+}
+
+int main() {
+        for (n = 0; fgets(map[n], M, stdin) != NULL; n++) ;
+
+        for (int i = 0; i < n; i++) {
+                clear(); walk(i, 0,   E); t = MAX(s, t);
+                clear(); walk(i, n-1, W); t = MAX(s, t);
+                clear(); walk(0,   i, S); t = MAX(s, t);
+                clear(); walk(n-1, i, N); t = MAX(s, t);
+        }
+
+        printf("%d\n", t);
+        return 0;
+}