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#advent of code 2024
#day 06
#cleaned up
grid = {};
xMin, yMin, xMax, yMax = 0, 0, 0, 0;
dirs = [(0,-1),(1,0),(0,1),(-1,0)];
d = 0; #starting direction of the guard
f = open("06.in","r");
for y, l in enumerate(f):
yMax = max(yMax,y);
for x, c in enumerate(l[:-1]):
xMax = max(xMax,x);
if c == "^":
guard1 = (x,y); #guard position
guard2 = (x,y); #guard pos for part 2
c = ".";
grid[(x,y)] = c;
f.close();
visited = set();
while True:
gx, gy = guard1; #split guard coordinates
dx, dy = dirs[d];
if not (xMin <= gx <= xMax)*(yMin <= gy <= yMax): break;
if grid.get((gx+dx,gy+dy),".") == "#":
d = (d+1)%4;
dx, dy = dirs[d];
visited.add(guard1);
guard1 = (gx+dx,gy+dy);
#definition of loop: if the guard meets the same obstacle twice, then he's looping
def bruteforce(NewPos,guard): #check if inserting in NewPos position an obstacle will create a loop
d = 0;
obstacles = set();
#register in set "obstacles" encountered obstacles in format: x,y,d,
#where d is the direction from which guard encountered the obstacle
ok = True
while True:
gx, gy = guard;
dx, dy = dirs[d];
if not (xMin <= gx+dy <= xMax)*(yMin <= gy+dy <= yMax):
ok = False; #if the guard left the grid then the new obstacle didnt work
break;
if grid.get((gx+dx,gy+dy),".") == "#" or (gx+dx,gy+dy)==NewPos:
d = (d+1)%4;
dx, dy = dirs[d];
if (guard,d) in obstacles: break;
obstacles.add((guard,d));
else:
guard = (gx+dx,gy+dy);
return ok;
NewPlaces = set(); #store the correct possibilites in a set just in case to prevent duplicates
for v in visited: #simulate another guard patrol for each possible new position v
if bruteforce(v,guard2): NewPlaces.add(v); #if he loops, +1 to score
part1 = len(visited);
part2 = len(NewPlaces);
print("part 1 =", part1);
print("part 2 =", part2);
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