day 6 part 2

.gitignore

@@ -1 +1,3 @@
 /cookie
+/*/sol
+/bin/

cron.sh

@@ -2,9 +2,9 @@
 set -euo pipefail
 
 # install me in your crontab!
-# 0 5 1-25 12 *     $HOME/adventofcode2023/cron.sh auto
+# 0 5 1-25 12 *     $HOME/adventofcode2024/cron.sh auto
 
-year=2023
+year=2024
 root=~/adventofcode${year}
 
 getinput() {

day05/sample1.in

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47

day05/sample2.in

@@ -0,0 +1,3 @@
+75,47,<em>61</em>,53,29
+97,61,<em>53</em>,29,13
+75,<em>29</em>,13

day05/sol.py

@@ -0,0 +1,77 @@
+import functools
+
+def parse(file):
+    rules = []
+    for line in file:
+        line = line.strip()
+        if line == "":
+            break
+        a, _, b = line.partition('|')
+        rules.append((a,b))
+    updates = []
+    for line in file:
+        line = line.strip()
+        updates.append(line.split(','))
+    return rules, updates
+
+def solve(file):
+    rules, updates = parse(file)
+    rules = set(rules)
+    def isvalid(pages):
+        for i in range(len(pages)):
+            p = pages[i]
+            for g in pages[i+1:]:
+                if (g,p) in rules:
+                    return False
+        return True
+
+    # part 1
+    t = 0
+    invalid = []
+    for pages in updates:
+        if isvalid(pages):
+            print(pages)
+            t += int(pages[len(pages)//2])
+        else:
+            invalid.append(pages)
+    print(t)
+
+    # part 2: select applicable rules and form a graph
+    # find the root node
+    # do a topological sort by doing a DFS of the graph
+    t = 0
+    for pages in invalid:
+        # select rules
+        rules2 = [(p,g) for p,g in rules if p in pages and g in pages]
+        #print(pages, rules2)
+
+        # find root node
+        S = set(p for p,g in rules2)
+        E = set(g for p,g in rules2)
+        top = next(iter(S-E))
+
+        # topological sort
+        l = []
+        seen = set()
+        def visit(node):
+            if node in seen: return
+            seen.add(node)
+            for p,g in rules2:
+                if p == node and g not in seen:
+                    visit(g)
+            l.append(node)
+        visit(top)
+        l.reverse()
+
+        # sanity check
+        assert len(l) == len(pages)
+        assert isvalid(l)
+        print(l)
+
+        # add middle number to total
+        t += int(l[len(l)//2])
+    print(t)
+
+
+solve(open("sample1.in"))
+solve(open("input"))

day06/Makefile

@@ -0,0 +1,2 @@
+CFLAGS=-O2 -std=c99 -ggdb -Wall -Wextra
+all: sol

day06/input

@@ -0,0 +1,130 @@
+....#.....#......#...............................#...........#.......#.....#................#...#....#....#................#..#.#.
+...................................................................................#...........#............#.....................
+..........#..............#.................................................#..............#.......................................
+....................#...............#...#.....................#..............................#....#.............................#.
+...............................##...............................................................#............#....................
+................#...........#................#...............#....#.......#.............................#..........#...........#..
+...........................#................................................#.##..................#.............#........#........
+......#......#.....#..........#.......................#..........#.............#.....................#........#....#..............
+..................................................#..................................#....#.........#...........#..............#..
+..................................#..................#..........................................#.........#....................#..
+#.................#....................#...........#....................................#......................#..................
+.......#..........................................................................................................#...............
+...............##.............................#...#.....................#..........................#.......................#......
+...#.......................................................#..........................................#...................#..#....
+.......#...#.......#.#.............#.....#.##.........................#...........................................................
+#................#.........#.......................##............................................#...#.....#........#.......#.....
+#......##..............................................................#......#....#....#....#.#...............#............#..#..
+.....#...............................##.......................................#.......#......#............................#.....#.
+.........#......#...............................#.....#.....#...................##......#.........................................
+.#.................................................#...............#........#............................#........................
+#.........#.........................................#.......................#..............#......................#...........#...
+..........................................##.............................................................##..#.......#............
+...#.........................#...........................................#........#...............................................
+#..................#............#.................................................................#.#....................#....#..#
+...................#.....................................#.#.........#.............#......#............................##.........
+....#..............................................................##.......................................................#....#
+.....................#.....#.............................................#.......................#..................#.............
+...........#.......................................#................#.........#...............#.#...........#.....#.....#........#
+.#..#.................#....#...............................#.................................................##...................
+..#.....#......#..........#...................#..#..................................................#.......#...#.................
+.............................................................#.......................#..........#.....#...................#.......
+.......#.......................#.#....#...#.....##.......................#.................................................#......
+.................#.....................#...............................................................#..#.......................
+...#.................#.#..................................................##......................................#..#............
+#........................................................#...#.........#................#.#.......................................
+.................#........#.#........................#.#..................................#.......................................
+..........#..#......#..................#.........................#................................#...............................
+.............................................................................................#....................................
+.....................#...........#........##.....#.........................#..............................#.....#....#............
+..#........#.........#.....................................................#......................................................
+...................................#...................#............#.............#...........................#...................
+....#.........................................................#................................#......#...#..#....................
+................................................................................#..#.......#..........................#....#......
+#...........................................................................#........................#............................
+..#..............#..........#...#..........................................................#......................................
+.......................................................#.................#.#....#.................#..........#....#...............
+..................................................................................................................................
+.................#.........................................................#..........#.........#.........#.................#.....
+....................#........#...................#................#...#....................#..............#................#......
+...#.............##........................................#.........#.................#...........#.........#....................
+................#............#...........#...............#.....................................#...........................#......
+....................................................#...........#..............................#..........#...........#...........
+.........#..............#................................#.............#......................................#.........#...#.....
+..#..#.........................................#.............................#....................................................
+.#............................##...#..........#............#..#.........................#......................#...#..............
+........#.....#..............#..................................................#...#......................#....#..............#..
+...............................................#.........#..................#............#.............................#..........
+..................................................................................................#....#..........................
+..............#..............................................................#....................................................
+.....#....#.....................#......................#...........#...#..#.............#.......................#.................
+.............................#...#..#...........................#............................................................#....
+.............................................#...............................#...................................................#
+..................................................................#......#....#.......................#.......#........#..........
+..................#.#.........................................................................................##.......#........#.
+.............................#.......................#.......................................##...................................
+.....#.............................................................................................................#.#............
+...............##.........#..#.....#...............#....................#.................................#.#....#................
+................#......................................................................#...............#...................#......
+.................#..............#.................................................................................................
+............#...#...........................................................................................#......#..............
+..#.....................................................................#.....#.#.#......#....#..........#........................
+.#........#.............................#.....................#.....................#....#........................................
+.......................................................................................................#..........................
+...#........#..................................................#.........................................................#......#.
+.......#.......#..#.................................................................................................#.............
+..............................#..#..........................#..#..................#.............#.................................
+..................#...#.............................................#...................#.......#...............#.................
+...#.......#........#.....................................#...........#.................................................#.........
+.#.............#....................................#........................................................##............#...#..
+...............#.....#....................................................................................#....#................#.
+....#...........................................................#.....#..............................................#............
+.........#..........#...........................#.......................................#....#....................#...............
+...............................................................#..........#......^...............................................#
+#..........................#.....................#..............................#..............................#..................
+...................#.....#......#...........#........#............#.......#.......#...............................................
+.....#.....#.............................................................#..............#........#..........................#....#
+............#...............................................................#.............#......................#................
+.....#...............................................##........................................#.......#......#...................
+.........................................#........................................................................................
+..........................#...............................#............#............................#.....#.......................
+...##.........#......#.....#...............................................................#........#.............................
+......#...............#.#......................#.......#..............................#...#.........#.........#..#.........#......
+....#......#....#........#.#.............................#......................................................#.....#...........
+.....#.............#.....................#...#...............#....................................................................
+......#............#............#.#............#....................#.............................................................
+.............#..................................................#....................#.............#.......#.............#........
+.............................................#......................................................................#.............
+...............................#............................................................#................#...................#
+............#.....#....................................................................................................#.#........
+.........................#....................#...##.......#............#..#.................................#......#.............
+....#......................#.....................#...........#.........................................#......#.#.................
+..................................................................#..........................#......................#.............
+.......................#......#..............................................................................#....................
+.......#.................#...............................##...............................................#.............#.........
+.#..............#.....................................................................................................#...........
+.......##.................#................#.#...#......................................#...............#...#.....................
+.............##......................................................#....................................#..........#............
+....................................#............#............#............#.....................................#................
+................#..#............................#..............................................#.....#...................#......#.
+....................#....#......#..................#................#.............................................................
+...............##...............#...#..........................#......#...............#..#................#.....#.............#...
+...........#..........#..........#..#.........#....#...#......#..............#................#....#..#...........................
+#.....................#..#...................................#...#..............................#......#.#.#......................
+............##...................#..#.............................................................................................
+..............................................#.#.......................#.................#....#..................#.......#.......
+....#................#......#........................................................#........#..............#....................
+.........#.#...............#............................###...........#...........................................................
+.........#.................................................................................#......#...#..............#......#.....
+....#....#......#.#.........#..........#...............#.........#............##.............#..#............................#....
+....#..#...#.....#...........................#.#.......................................#...#.....................#............#..#
+...........#............................#........#...#......#...............................................#...#.................
+..#...............................................................#..............................................#.........#......
+...................#.....................................#....................................#.#.#............#............#.....
+.....#.................#...........................##.................#..#........................................................
+...#.......#...................................#.............................#...........#......##.#...#.........#.#...........#..
+.#.............#......#..#...#......................................................#..............#.............#.#..............
+.......................#............#...................#.....................#.......................#.............#..#......#...
+......................#..#.#.......#........#....#.............#.........#..............................#.#..........#........#...
+.................#.............#..#..........#...#.........#..................................#..#.............#................#.
+.#..................................#....#...........................................#..............................#...#.........

day06/sample1.in

@@ -0,0 +1,10 @@
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...

day06/sample2.in

@@ -0,0 +1,10 @@
+....#.....
+....^....#
+..........
+..#.......
+.......#..
+..........
+.#........
+........#.
+#.........
+......#...

day06/sample3.in

@@ -0,0 +1,10 @@
+....#.....
+........>#
+..........
+..#.......
+.......#..
+..........
+.#........
+........#.
+#.........
+......#...

day06/sample4.in

@@ -0,0 +1,10 @@
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#......v.
+........#.
+#.........
+......#...

day06/sample5.in

@@ -0,0 +1,10 @@
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#........
+........#.
+#.........
+......#v..

day06/sample6.in

@@ -0,0 +1,10 @@
+....#.....
+....XXXXX#
+....X...X.
+..#.X...X.
+..XXXXX#X.
+..X.X.X.X.
+.#XXXXXXX.
+.XXXXXXX#.
+#XXXXXXX..
+......#X..

day06/sol.c

@@ -0,0 +1,214 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <stdbool.h>
+
+struct grid {
+	char** A;
+	int x, y;
+};
+
+void* xrealloc(void* ptr, size_t size) {
+	if (size == 0) {
+		size = 1;
+	}
+	ptr = realloc(ptr, size);
+	if (ptr == NULL) {
+		fprintf(stderr, "fatal: alloc(%zd) failed", size);
+		exit(1);
+	}
+	return ptr;
+}
+
+int readfile(const char* filename, struct grid* out) {
+	FILE *fp = fopen(filename, "r");
+	if (fp == NULL) {
+		perror("fopen");
+		exit(1);
+	}
+
+	int len = 0;
+	int cap = 100;
+	char* data = xrealloc(NULL, cap);
+	for (;;) {
+		if (len >= cap) {
+			cap *= 2;
+			data = xrealloc(data, cap);
+		}
+		int c = fgetc(fp);
+		if (c == -1) {
+			break;
+		}
+		data[len] = c;
+		len++;
+	}
+	int i, nl=0;
+	for (i = 0; i < len; i++) {
+		if (data[i] == '\n') {
+			nl++;
+		}
+	}
+	// split on newlines
+	char** lines = xrealloc(NULL, nl * sizeof(char*));
+	char* p = data;
+	int mincol = INT_MAX;
+	i = 0;
+	while (p != NULL && p < data+len) {
+		lines[i++] = p;
+		char* q = memchr(p, '\n', (data+len)-p);
+		if (!q) {
+			break; // TODO: final line?
+		}
+		int col = q - p;
+		if (mincol > col && col > 0) {
+			mincol = col;
+		}
+		p = q+1; // skip newline
+	}
+
+	out->A = lines;
+	out->x = mincol;
+	out->y = nl;
+
+	return 0;
+}
+
+inline bool inbounds(struct grid *g, int x, int y) {
+	return (0 <= x && x < g->x && 0 <= y && y < g->y);
+}
+
+struct step_r { int x, y, dx, dy; bool ok; };
+struct step_r step(struct grid *g, int x, int y, int dx, int dy) {
+	struct step_r r = {0};
+	if (!inbounds(g, x, y)) {
+		return r;
+	}
+	// if there is nothing in front of you, step forward
+	if (!inbounds(g, x+dx, y+dy) || g->A[y+dy][x+dx] != '#') {
+		r.x = x+dx;
+		r.y = y+dy;
+		r.dx = dx;
+		r.dy = dy;
+		r.ok = true;
+		return r;
+	} else {
+		// if there is something in front of you, turn right
+		r.x = x;
+		r.y = y;
+		r.dx = -dy;
+		r.dy = dx;
+		r.ok = true;
+		return r;
+	}
+}
+
+struct point { int x, y; };
+struct point startingPoint(struct grid *g) {
+	int x, y;
+	for (y = 0; y < g->y; y++)
+	for (x = 0; x < g->x; x++) {
+		if (g->A[y][x] == '^') {
+			struct point r = {x, y};
+			return r;
+		}
+	}
+	struct point r = {-1,-1};
+	return r;
+}
+
+int solve(struct grid *g) {
+	struct point start = startingPoint(g);
+	int x = start.x, y = start.y;
+	int count = 0;
+	int dx = 0, dy = -1; // up
+	while(inbounds(g, x, y)) {
+		if (g->A[y][x] != 'x') {
+			count++;
+		}
+		g->A[y][x] = 'x';
+
+		struct step_r r = step(g, x, y, dx, dy);
+		if (r.ok != true) {
+			break;
+		}
+		x = r.x;
+		y = r.y;
+		dx = r.dx;
+		dy = r.dy;
+	}
+	g->A[start.y][start.x] = '^';
+	printf("%d\n", count);
+	return 0;
+}
+
+// returns whether the chosen grid will cause the guard to get stuck in a loop
+bool loops(struct grid *g, struct point start, uint16_t* state) {
+	int x = start.x;
+	int y = start.y;
+	int dx = 0, dy = -1; // up
+	int stride = g->x;
+	//printf("loops(%d,%d)\n", x,y);
+	while(inbounds(g, x, y)) {
+		uint16_t dir = 15;
+		if (dx == 1) { dir = 1; }
+		else if (dx == -1) { dir = 2; }
+		else if (dy == 1) { dir = 4; }
+		else if (dy == -1) { dir = 8; }
+
+		uint16_t *s = &state[y*stride + x];
+		if ((*s & dir) != 0) {
+			// revisited a state, loop!
+			return true;
+		}
+		*s |= dir;
+
+		struct step_r r = step(g, x, y, dx, dy);
+		if (r.ok != true) {
+			// step failed, no loop
+			return false;
+		}
+		x = r.x;
+		y = r.y;
+		dx = r.dx;
+		dy = r.dy;
+	}
+	// left the map, no loop
+	return false;
+}
+
+
+int solve2(struct grid *g) {
+	int count = 0;
+	int ox, oy; // obstacle coords
+	struct point p = startingPoint(g);
+	size_t state_size = g->x * g->y * sizeof(uint16_t);
+	uint16_t *state = xrealloc(NULL, state_size);
+	for (oy = 0; oy < g->y; oy++)
+	for (ox = 0; ox < g->x; ox++) {
+		int c = g->A[oy][ox];
+		if (c != '#' && c != '^') {
+			g->A[oy][ox] = '#';
+			memset(state, 0, state_size);
+			if (loops(g, p, state)) {
+				count++;
+			}
+			g->A[oy][ox] = c;
+		}
+	}
+	free(state);
+	printf("%d\n", count);
+	return 0;
+}
+
+
+int main() {
+	struct grid g;
+	//readfile("sample1.in", &g);
+	readfile("input", &g);
+	printf("%d %d\n", g.x, g.y);
+	solve(&g);
+	//printf("%s", g.A[0]);
+	solve2(&g);
+}