aoc_2022_day_24_tf.py

# aoc_2022_day_24_tf.py
from collections import *
import math, sys, copy, functools, json, re
# In one minute, each blizzard moves one position in the direction it is pointing:
DIRS = [(0,-1),(-1,0),(0,1),(1,0)]
blizzards = defaultdict(list) # pos to direction
# f = open("day24.input")
f = open("day24_2.input")
grid = []
for line in f:
  line = line.strip()
  grid.append(list(line))
  print(line)
f.close()

BZ_TO_DIR = {
  '<': (0,-1),
  '>': (0,1),
  '^': (-1, 0),
  'v': (1,0)
}

m,n = len(grid), len(grid[0])

def inb(r, c):
  return 1<=r<m-1 and 1<=c<n-1

def dbg_grid_2():
  print("---dbg2 s")
  for i in range(m):
    row = ""
    for j in range(n):
      if inb(i, j):
        row += str(len(blizzards[(i,j)])) if blizzards[(i,j)] else '.'
      else:
        row += grid[i][j]
    print(row)
  print("---dbg2 end")

for i in range(m):
  for j in range(n):
    if grid[i][j] in '<>^v':
      dr, dc = BZ_TO_DIR[grid[i][j]]
      blizzards[ (i,j) ].append( (dr, dc) )

def move_blizzards():
#   global blizzards
  bzx = defaultdict(list)
  for r, c in list(blizzards.keys()):
    for dr, dc in blizzards[(r, c)]:
      nr =  ( ( (r -1 ) + dr ) % ( (m) - 2) ) + 1
      nc = ( ( (c -1 ) + dc ) % ( (n) - 2) ) + 1
      bzx[(nr,nc)].append( (dr, dc) )
#   blizzards = bzx
  return bzx

def can_wait(pr, pc, nbz):
    for r, c in nbz.keys():
        if (pr, pc) == (r,c):
            return False
    return True

def test(sr, sc, tr, tc):
  global blizzards
  visited = set()
  visited.add( (sr, sc, 0) )
  q = deque()
  q.append( (sr, sc, 0) )

  moves = 0
  while q:
    print("moves!", moves, end="\r")
  #   print("curr!!", moves, q)
    # print("size of q", len(q), moves, end="\r")
    # print(blizzards)

    nbz = move_blizzards()
    for _ in range(len(q)):
      r, c, min = q.popleft()
      if (r, c) == (tr, tc):
        print('reached', (r, c), moves, min)
      #   dbg_grid_2()
        return moves
        # sys.exit()
      
      for dr, dc in DIRS:
        nr, nc = r+dr, c+dc
        if (nr, nc) == (tr, tc):
          q.append((nr, nc, min+1)) # special case
          break # no need to cont
        if not inb(nr, nc): continue
        if not can_wait(nr, nc, nbz): 
          continue

        if (nr, nc, min + 1) not in visited:
          visited.add((nr, nc, min + 1))
          q.append( (nr, nc, min + 1) )
          # appended = True
      
      if  can_wait(r, c, nbz):
        # check if you can wait / there is a blizzard headed towards you!!!
        # you cannot share a position with a blizzard
        if (r, c, min + 1) not in visited:
          visited.add((r, c, min + 1))
          q.append( (r, c, min + 1) )

    blizzards = nbz
    moves += 1

a = (test(0,1, m-1, n-2))
b = (test(m-1, n-2, 0,1))
c = (test(0,1, m-1, n-2))
print(a,b,c, a+b+c)