From feca43e796fbe8bde441f017f4c94642392bc40f Mon Sep 17 00:00:00 2001
From: Thomas Voss <thomasvoss@live.com>
Date: Thu, 2 Dec 2021 14:34:48 +0100
Subject: Add day 23 solutions

---
 2015/23/puzzles.l | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 2015/23/puzzles.l

(limited to '2015/23/puzzles.l')

diff --git a/2015/23/puzzles.l b/2015/23/puzzles.l
new file mode 100644
index 0000000..7d654e1
--- /dev/null
+++ b/2015/23/puzzles.l
@@ -0,0 +1,103 @@
+%{
+#define _POSIX_C_SOURCE
+#include <err.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/* Shut up the compiler */
+int fileno(FILE *);
+
+struct Instr {
+	enum {
+		HLF,
+		INC,
+		JIE,
+		JIO,
+		JMP,
+		TPL
+	} type;
+	enum {
+		A,
+		B
+	} reg;
+	int imm;
+};
+
+int i = 0;
+struct Instr *program;
+
+#ifdef PART2
+unsigned long long registers[2] = {1, 0};
+#else
+unsigned long long registers[2];
+#endif
+%}
+
+%x ARGS
+
+%%
+
+hlf	{ program[i].type = HLF; BEGIN(ARGS); }
+inc	{ program[i].type = INC; BEGIN(ARGS); }
+jie	{ program[i].type = JIE; BEGIN(ARGS); }
+jio	{ program[i].type = JIO; BEGIN(ARGS); }
+jmp	{ program[i].type = JMP; BEGIN(ARGS); }
+tpl	{ program[i].type = TPL; BEGIN(ARGS); }
+
+<ARGS>[ab]		{ program[i].reg = *yytext - 'a'; }
+<ARGS>[+\-][0-9]+	{ program[i].imm = atoi(yytext); }
+<ARGS>[ ,]+		{ ; }
+<ARGS>\n		{ i++; BEGIN(INITIAL); }
+
+%%
+
+static unsigned long long
+execute(void)
+{
+	for (i = 0; i < PROGLEN; i++) {
+		switch (program[i].type) {
+		case HLF:
+			registers[program[i].reg] /= 2;
+			break;
+		case INC:
+			registers[program[i].reg]++;
+			break;
+		case JIE:
+			if (!(registers[program[i].reg] & 1))
+				i += program[i].imm - 1;
+			break;
+		case JIO:
+			if (registers[program[i].reg] == 1)
+				i += program[i].imm - 1;
+			break;
+		case JMP:
+			i += program[i].imm - 1;
+			break;
+		case TPL:
+			registers[program[i].reg] *= 3;
+			break;
+		}
+	}
+
+	return registers[B];
+}
+
+int
+main(void)
+{
+	FILE *fp;
+
+	if (!(program = calloc(PROGLEN, sizeof(struct Instr))))
+		err(EXIT_FAILURE, "calloc");
+
+	if (!(fp = fopen("input", "r")))
+		err(EXIT_FAILURE, "fopen");
+
+	yyrestart(fp);
+	yylex();
+	fclose(fp);
+
+	printf("%llu\n", execute());
+	return EXIT_SUCCESS;
+}
-- 
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