day 6 part 1

day06/Makefile

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+CFLAGS=-O2 -std=c99 -Wall -Wextra
+all: sol

day06/input

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day06/sample1.in

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+.........#
+..........
+..#.......
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+..........
+.#..^.....
+........#.
+#.........
+......#...

day06/sample2.in

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+..........
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+..........
+.#........
+........#.
+#.........
+......#...

day06/sample3.in

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+........>#
+..........
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+..........
+.#........
+........#.
+#.........
+......#...

day06/sample4.in

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+....#.....
+.........#
+..........
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+..........
+.#......v.
+........#.
+#.........
+......#...

day06/sample5.in

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+..........
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+..........
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+........#.
+#.........
+......#v..

day06/sample6.in

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+....#.....
+....XXXXX#
+....X...X.
+..#.X...X.
+..XXXXX#X.
+..X.X.X.X.
+.#XXXXXXX.
+.XXXXXXX#.
+#XXXXXXX..
+......#X..

day06/sol.c

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+#include <stdlib.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) {
+	int i;
+	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;
+	}
+}
+
+
+int solve(struct grid *g) {
+	int x, y;
+	int cx = -1, cy = -1;
+	int count = 0;
+	for (y = 0; y < g->y; y++)
+	for (x = 0; x < g->x; x++) {
+		if (g->A[y][x] == '^') {
+			cx = x;
+			cy = y;
+			break;
+		}
+	}
+	int dx = 0, dy = -1; // up
+	while(inbounds(g, cx, cy)) {
+		if (g->A[cy][cx] != 'x') {
+			count++;
+		}
+		g->A[cy][cx] = 'x';
+
+		struct step_r r = step(g, cx, cy, dx, dy);
+		if (r.ok != true) {
+			break;
+		}
+		cx = r.x;
+		cy = r.y;
+		dx = r.dx;
+		dy = r.dy;
+	}
+	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);
+	//solve2(&g);
+	printf("%s", g.A[0]);
+}