Day 15: Warehouse Woes

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  • sjmulder@lemmy.sdf.org
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    8 days ago

    C

    3h+ train ride back home from weekend trip but a little tired and not feeling it much. Finished part 1, saw that part 2 was fiddly programming, left it there.

    Finally hacked together something before bed. The part 2 twist required rewriting the push function to be recursive but also a little care and debugging to get that right. Cleaned it up over lunch, happy enough with the solution now!

    Code
    #include "common.h"
    
    #define GW 104
    #define GH 52
    
    struct world { char g[GH][GW]; int px,py; };
    
    static int
    can_clear(struct world *w, int x, int y, int dx, int dy)
    {
    	assert(x>=0); assert(x<GW);
    	assert(y>=0); assert(y<GH);
    	assert((dx && !dy) || (dy && !dx));
    
    	return
    	    (x+dx >= 0 || x+dx < GW) &&
    	    (y+dy >= 0 || y+dy < GW) &&
    	    (w->g[y][x] == '.' || (
    	     w->g[y][x] != '#' && can_clear(w, x+dx,y+dy, dx,dy) &&
    	     (!dy || w->g[y][x]!='[' || can_clear(w, x+1,y+dy, 0,dy)) &&
    	     (!dy || w->g[y][x]!=']' || can_clear(w, x-1,y,    0,dy)) &&
    	     (!dy || w->g[y][x]!=']' || can_clear(w, x-1,y+dy, 0,dy))));
    }
    
    /* check can_clear() first! */
    static void
    clear(struct world *w, int x, int y, int dx, int dy)
    {
    	assert(x>=0); assert(x<GW); assert(x+dx>=0); assert(x+dx<GW);
    	assert(y>=0); assert(y<GH); assert(y+dy>=0); assert(y+dy<GH);
    
    	if (w->g[y][x] == '.')
    		return;
    	if (dy && w->g[y][x] == ']')
    		{ clear(w, x-1,y, dx,dy); return; }
    
    	if (dy && w->g[y][x] == '[') {
    		clear(w, x+1,y+dy, dx,dy);
    		w->g[y+dy][x+dx+1] = ']';
    		w->g[y][x+1] = '.';
    	}
    
    	clear(w, x+dx,y+dy, dx,dy);
    	w->g[y+dy][x+dx] = w->g[y][x];
    	w->g[y][x] = '.';
    }
    
    static void
    move(struct world *w, int dx, int dy)
    {
    	if (can_clear(w, w->px+dx, w->py+dy, dx,dy)) {
    		clear(w, w->px+dx, w->py+dy, dx,dy);
    		w->px += dx;
    		w->py += dy;
    	}
    }
    
    static int
    score(struct world *w)
    {
    	int acc=0, x,y;
    
    	for (y=0; y<GH && w->g[y][0]; y++)
    	for (x=0; x<GW && w->g[y][x]; x++)
    		if (w->g[y][x] == 'O' || w->g[y][x] == '[')
    			acc += 100*y + x;
    
    	return acc;
    }
    
    int
    main(int argc, char **argv)
    {
    	static struct world w1,w2;
    	int x,y, c;
    	char *p;
    
    	if (argc > 1)
    		DISCARD(freopen(argv[1], "r", stdin));
    
    	for (y=0; fgets(w1.g[y], GW, stdin); y++) {
    		if (!w1.g[y][0] || w1.g[y][0]=='\n')
    			break;
    
    		assert(y+1 < GH);
    		assert(strlen(w1.g[y])*2+1 < GW);
    
    		for (x=0; w1.g[y][x]; x++)
    			if (w1.g[y][x] == 'O') {
    				w2.g[y][x*2]   = '[';
    				w2.g[y][x*2+1] = ']';
    			} else {
    				w2.g[y][x*2]   = w1.g[y][x];
    				w2.g[y][x*2+1] = w1.g[y][x];
    			}
    
    		if ((p = strchr(w1.g[y], '@'))) {
    			w1.py = y; w1.px = p-w1.g[y];
    			w2.py = y; w2.px = w1.px*2;
    
    			w1.g[w1.py][w1.px]   = '.';
    			w2.g[w2.py][w2.px]   = '.';
    			w2.g[w2.py][w2.px+1] = '.';
    		}
    	}
    
    	while ((c = getchar()) != EOF)
    		switch (c) {
    		case '^': move(&w1, 0,-1); move(&w2, 0,-1); break;
    		case 'v': move(&w1, 0, 1); move(&w2, 0, 1); break;
    		case '<': move(&w1,-1, 0); move(&w2,-1, 0); break;
    		case '>': move(&w1, 1, 0); move(&w2, 1, 0); break;
    		}
    
    	printf("15: %d %d\n", score(&w1), score(&w2));
    	return 0;
    }
    

    https://github.com/sjmulder/aoc/blob/master/2024/c/day15.c