adventofcode

commit: 0749a939bc1e50f0c05782038fbb3dbc11979286
parent 663cfb69b719219101950155cdcb429232355ae1
Author: Haelwenn (lanodan) Monnier <contact@hacktivis.me>
Date:   Mon,  1 Dec 2025 20:24:35 +0100

day1_2: add

Diffstat:
M
Makefile
3
+++
A
day1_2.c
85
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 88 insertions(+), 0 deletions(-)
diff --git a/Makefile b/Makefile
@@ -7,4 +7,7 @@ CFLAGS ?= -g -Wall -Wextra
 .c:
 	$(CC) -std=c11 $(CFLAGS) -o $@ $^ $(LDFLAGS) $(LDSTATIC)
 
+all: day1 day1_2
+
 day1: day1.c
+day1_2: day1_2.c
diff --git a/day1_2.c b/day1_2.c
@@ -0,0 +1,85 @@
+// SPDX-FileCopyrightText: 2025 Haelwenn (lanodan) Monnier
+// SPDX-License-Identifier: BSD-3-Clause
+
+#define _POSIX_C_SOURCE 202405L
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+
+int
+main(void)
+{
+	int pos = 50; // The dial starts by pointing at 50
+	int pass = 0;
+
+	char *line = NULL;
+	size_t linez = 0;
+	while(1)
+	{
+		errno = 0;
+		ssize_t nread = getline(&line, &linez, stdin);
+		if(nread < 0)
+		{
+			if(errno != 0)
+			{
+				perror("getline");
+				free(line);
+				return 1;
+			}
+
+			break;
+		}
+
+		if(line[nread-1] == '\n')
+			line[nread-1] = '\0';
+
+		if(line[0] != 'L' && line[0] != 'R')
+		{
+			fprintf(stderr, "Got %c instead of [LR]\n", line[0]);
+			free(line);
+			return 1;
+		}
+
+		if(line[1] < '0' || line[1] > '9')
+		{
+			fprintf(stderr, "Got %c instead of [0-9] as first digit\n", line[0]);
+			free(line);
+			return 1;
+		}
+		int rot = line[1] - '0';
+
+		for(int i = 2; i < nread; i++)
+		{
+			if(line[i] < '0' || line[i] > '9') break;
+
+			rot = (rot*10) + (line[i] - '0');
+		}
+
+		/* brute-force it rather than math it out */
+		switch(line[0])
+		{
+		case 'L':
+			for(int a = rot; a > 0; a--)
+			{
+				pos = pos == 0 ? 99 : pos-1;
+
+				if(pos == 0) pass++;
+			}
+			break;
+		case 'R':
+			for(int a = rot; a > 0; a--)
+			{
+				pos = pos == 99 ? 0 : pos+1;
+
+				if(pos == 0) pass++;
+			}
+			break;
+		}
+
+		printf("%-4s rot:%-4d pos:%-2d pass:%d\n", line, rot, pos, pass);
+	}
+	free(line);
+
+	printf("Result: %d\n", pass);
+}