1 files changed, 62 insertions, 0 deletions
diff --git a/10.c b/10.c
new file mode 100644
index 0000000..a5e3d8e
--- /dev/null
+++ b/10.c
@@ -0,0 +1,62 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+int
+main()
+{
+	int cycle;
+	char buf[BUFSIZ];
+	char * op, * arg;
+	int opcycles = 0;
+	int rx = 1, nextread = 20, interval = 40, total = 0;
+
+	for (cycle = 1; cycle <= 220; ++cycle) {
+		// Start of cycle. Do we need to read a new instruction?
+		if (opcycles == 0) {
+			char * toksave = NULL;
+
+			if (!fgets(buf, sizeof(buf), stdin))
+				break;
+
+			op = strtok_r(buf, " \n", &toksave);
+			arg = strtok_r(NULL, "\n", &toksave);
+
+			// Just read instruction. Set op cycle count, and
+			// perform any immediate actions
+			if (strcmp(op, "noop") == 0 && !arg) {
+				opcycles = 1;
+			}
+			else if (strcmp(op, "addx") == 0 && arg) {
+				opcycles = 2;
+			}
+			else {
+				fprintf(stderr, "Unexpected op/arg: %s/%s\n", op, arg ? arg : "(null)");
+				return -1;
+			}
+		}
+
+		// Mid-cycle debugger attachment.
+		if (cycle >= nextread) {
+			total += rx * cycle;
+			nextread += interval;
+		}
+
+		// Perform cycle. Reduce opcycle count, do actions that occur on
+		// op completion and increment cycle counter.
+		--opcycles;
+
+		if (opcycles == 0) {
+			if (strcmp(op, "addx") == 0) {
+				rx += atoi(arg);
+			}
+		}
+	}
+
+	printf("Sum of interesting signal strengths: %d\n", total);
+
+	return 0;
+}
+