From 85d874b1a28bf849f4d64d94a0a807940f443618 Mon Sep 17 00:00:00 2001
From: "C. McEnroe" <june@causal.agency>
Date: Sat, 7 Dec 2019 15:46:42 -0500
Subject: Solve day 7 part 1

---
 2019/day07.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 2019/day07.c

diff --git a/2019/day07.c b/2019/day07.c
new file mode 100644
index 0000000..d921683
--- /dev/null
+++ b/2019/day07.c
@@ -0,0 +1,64 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Intcode {
+	int ip;
+	int mode[3];
+	int mem[1024];
+	int in[2];
+	int out;
+};
+
+static int *p(struct Intcode *m, int i) {
+	return (m->mode[i - 1] ? &m->mem[m->ip + i] : &m->mem[m->mem[m->ip + i]]);
+}
+
+static void run(struct Intcode *m) {
+	while (m->mem[m->ip] != 99) {
+		m->mode[0] = m->mem[m->ip] / 100 % 10;
+		m->mode[1] = m->mem[m->ip] / 1000 % 10;
+		m->mode[2] = m->mem[m->ip] / 10000 % 10;
+		switch (m->mem[m->ip] % 100) {
+			break; case 1: *p(m, 3) = *p(m, 1) + *p(m, 2); m->ip += 4;
+			break; case 2: *p(m, 3) = *p(m, 1) * *p(m, 2); m->ip += 4;
+			break; case 3: *p(m, 1) = m->in[0]; m->in[0] = m->in[1]; m->ip += 2;
+			break; case 4: m->out = *p(m, 1); m->ip += 2;
+			break; case 5: m->ip = (*p(m, 1) ? *p(m, 2) : m->ip + 3);
+			break; case 6: m->ip = (*p(m, 1) ? m->ip + 3 : *p(m, 2));
+			break; case 7: *p(m, 3) = (*p(m, 1) < *p(m, 2)); m->ip += 4;
+			break; case 8: *p(m, 3) = (*p(m, 1) == *p(m, 2)); m->ip += 4;
+			break; default: abort();
+		}
+	}
+}
+
+int main(void) {
+	int mem[1024] = {0};
+	for (int i = 0; EOF != scanf("%d,", &mem[i]); ++i);
+
+	struct Intcode amp[5] = {0};
+	int max = 0;
+	for (int p = 0; p <= 044444; ++p) {
+		int x = p;
+		for (int i = 0; i < 5; ++i) {
+			amp[i].in[0] = x & 7;
+			x >>= 3;
+		}
+		for (int i = 0; i < 5; ++i) {
+			if (amp[i].in[0] > 4) goto skip;
+			for (int j = 0; j < 5; ++j) {
+				if (i != j && amp[i].in[0] == amp[j].in[0]) goto skip;
+			}
+		}
+		for (int i = 0; i < 5; ++i) {
+			amp[i].ip = 0;
+			memcpy(amp[i].mem, mem, sizeof(amp[i].mem));
+			amp[i].in[1] = (i ? amp[i - 1].out : 0);
+			run(&amp[i]);
+		}
+		if (amp[4].out > max) max = amp[4].out;
+skip:;
+	}
+	printf("%d\n", max);
+}
-- 
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