Move all Advent of Codes into one repo

1 files changed, 95 insertions, 0 deletions

diff --git a/2020/05/part2.c b/2020/05/part2.c
new file mode 100644
index 0000000..396ea76
--- /dev/null
+++ b/2020/05/part2.c
@@ -0,0 +1,95 @@
+#include <stdio.h>
+
+#define COLUMNS 8
+#define ROWS 128
+
+int seat_id(const char *seat)
+{
+    int row = 0;
+    int row_lower = 0;
+    int row_upper = ROWS - 1;
+    int column = 0;
+    int column_lower = 0;
+    int column_upper = COLUMNS - 1;
+    int i = 0;
+    for (; i < 6; i++) {
+        switch (seat[i]) {
+            case 'F':
+                row_upper -= (row_upper - row_lower + 1) / 2;
+                break;
+            case 'B':
+                row_lower += (row_upper - row_lower + 1) / 2;
+                break;
+        }
+    }
+
+    switch (seat[i++]) {
+        case 'F':
+            row = row_lower;
+            break;
+        case 'B':
+            row = row_upper;
+            break;
+    }
+
+    for (; i < 9; i++) {
+        switch (seat[i]) {
+            case 'L':
+                column_upper -= (column_upper - column_lower + 1) / 2;
+                break;
+            case 'R':
+                column_lower += (column_upper - column_lower + 1) / 2;
+                break;
+        }
+    }
+
+    switch (seat[i++]) {
+        case 'L':
+            column = column_lower;
+            break;
+        case 'R':
+            column = column_upper;
+            break;
+    }
+
+    return row * COLUMNS + column;
+}
+
+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;
+    }
+
+    fclose(file);
+
+    for (int i = min + 1; i < max; i++) {
+        if (table[i] == 0) {
+            return i;
+        }
+    }
+
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    printf("%i", missing_seat_id(argv[argc - 1]));
+}