1 files changed, 90 insertions, 0 deletions
diff --git a/2020/05/part2_fast.c b/2020/05/part2_fast.c
new file mode 100644
index 0000000..483dd8f
--- /dev/null
+++ b/2020/05/part2_fast.c
@@ -0,0 +1,90 @@
+#include <stdio.h>
+
+#define COLUMNS 8
+#define ROWS 128
+
+int row(const char *seat)
+{
+    int end_res = 0;
+    for (int i = 0; i < 7; i++) {
+        if (seat[i] == 'B') {
+            end_res |= 0x40 >> i;
+        }
+    }
+
+    return end_res;
+}
+
+int column(const char *seat)
+{
+    int end_res = 0;
+    for (int i = 7; i < 10; i++) {
+        if (seat[i] == 'R') {
+            end_res |= 0x200 >> i;
+        }
+    }
+
+    return end_res;
+}
+
+#ifdef USE_ASM
+int seat_id(const char *seat);
+#else
+int seat_id(const char *seat)
+{
+    int end_res = 0;
+    int i = 0;
+    for (; i < 7; i++) {
+        if (seat[i] == 'B') {
+            end_res |= 0x200 >> i;
+        }
+    }
+
+    for (; i < 10; i++) {
+        if (seat[i] == 'R') {
+            end_res |= 0x200 >> i;
+        }
+    }
+
+    return end_res;
+}
+#endif
+
+int missing_seat_id(const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    char table[COLUMNS * ROWS] = { 0 };
+
+    // Include space for newline and string terminator
+    char buffer[16] = { 0 };
+
+    int min = __INT_MAX__;
+    int max = 0;
+    while (fgets(buffer, 16, file)) {
+        int tmp = seat_id(buffer);
+        if (tmp < min) {
+            min = tmp;
+        }
+        else if (tmp > max) {
+            max = tmp;
+        }
+
+        table[tmp] = 1;
+    }
+
+    for (int i = min + 1; i < max; i++) {
+        if (table[i] == 0) {
+            return i;
+        }
+    }
+
+    fclose(file);
+
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%i", missing_seat_id(argv[argc - 1]));
+}