1 files changed, 41 insertions, 0 deletions
diff --git a/2020/03/part2.c b/2020/03/part2.c
new file mode 100644
index 0000000..bae8654
--- /dev/null
+++ b/2020/03/part2.c
@@ -0,0 +1,41 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int count_trees(int inc_right, int inc_down, const char *filename)
+{
+    FILE *file = fopen(filename, "r");
+
+    // Include space for newline and string terminator
+    char buffer[64] = { 0 };
+    // Start is always safe
+    fgets(buffer, 64, file);
+    // strlen includes the newline
+    int width = strchr(buffer, '\n') - buffer;
+
+    int pos = inc_right;
+    int hit = 0;
+    for (int i = 1; fgets(buffer, 64, file); i++) {
+        if (inc_down != 1 && i % inc_down != 0) {
+            continue;
+        }
+
+        if (buffer[pos] == '#') {
+            hit++;
+        }
+
+        pos = (pos + inc_right) % width;
+    }
+
+    fclose(file);
+
+    return hit;
+}
+
+int main(int argc, char *argv[])
+{
+    char *arg = argv[argc - 1];
+    long mul = (long)count_trees(1, 1, arg) * count_trees(3, 1, arg) * count_trees(5, 1, arg) * count_trees(7, 1, arg) * count_trees(1, 2, arg);
+    printf("%li\n", mul);
+}