Solution to day 23, in C.

2017/day-23/solution.c

@@ -0,0 +1,98 @@
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAX_INSTR 1000
+
+#define SETVAL
+
+typedef struct {
+	char op[4];
+	char op_a[2];
+	char op_b[10];
+} instr_t;
+
+int get_val(const char* identifier, const int* registers)
+{
+	if (isalpha(identifier[0])) {
+		return registers[identifier[0] - 'a'];
+	} else {
+		return atoi(identifier);
+	}
+}
+
+int run_program(const instr_t program[], const int max_instr, int registers[])
+{
+	int iptr = 0;
+	int muls = 0;
+	while (iptr < max_instr) {
+		instr_t const* cur = &program[iptr];
+		int op_b = get_val(cur->op_b, registers);
+
+		int* res = &registers[cur->op_a[0] - 'a'];
+
+		if (!strcmp(cur->op, "set")) {
+			*res = op_b;
+		} else if (!strcmp(cur->op, "sub")) {
+			*res -= op_b;
+		} else if (!strcmp(cur->op, "mul")) {
+			*res *= op_b;
+			++muls;
+		} else if (!strcmp(cur->op, "jnz")) {
+			if (get_val(cur->op_a, registers) != 0) {
+				iptr += op_b;
+				continue;
+			}
+		}
+		iptr += 1;
+	}
+
+	return muls;
+}
+
+int is_prime(long long int num) {
+	for (long long int i = 2; i * i <= num; ++i) {
+		if (num % i == 0) {
+			return 0;
+		}
+	}
+
+	return 1;
+}
+
+int run_optimized()
+{
+	int b = 84 * 100 + 100000;
+	int c = b + 17000;
+	int h = 0;
+
+	for (; b <= c; b += 17) {
+		// Test if B is prime, result = f == 1;
+		if (!is_prime(b)) {
+			h += 1;
+		}
+	}
+
+	return h;
+}
+
+int main()
+{
+	instr_t program[MAX_INSTR];
+	int max_instr = 0;
+
+	int debug_registers[8] = {0};
+
+	while (scanf("%s %s %s", program[max_instr].op, program[max_instr].op_a, program[max_instr].op_b) != EOF) {
+		++max_instr;
+	}
+
+	int muls = run_program(program, max_instr, debug_registers);
+	printf("Muls executed: %d\n", muls);
+
+	printf("Final value of 'h': %d\n", run_optimized());
+
+	return 0;
+}