#!/usr/bin/env python

# https://adventofcode.com/2025/day/7


def read_input(filename: str = "day07input.txt") -> list[list[str]]:
  f = open(filename, "r")
  lines = [l.strip("\n") for l in f.readlines()]
  return [list(line) for line in lines]


# for part 1 we're using a top-down approach 
def beam1(row: int, col: int) -> int:
  # make sure we're inside the field
  assert 0 <= row <= len(field) - 1
  assert 0 <= col <= len(field[0])

  split_count = 0

  while row < len(field):
    # continue down from starting position
    if field[row][col] == "S":
      row += 1
    # continue down through empty space
    elif field[row][col] == ".":
      field[row][col] = "|"
      row += 1
    # stop if we're hitting a previous beam 
    elif field[row][col] == "|":
      break

    # split beam
    elif field[row][col] == "^":
#      print(f"splitting beam at {row=} and {col=}")
      split_count += 1
      # left beam
      if col > 0:
        split_count += beam1(row, col - 1)
      # right beam
      if col + 1 < len(field[0]):
        split_count += beam1(row, col + 1)
      # stop current beam
      break

    else:
      raise Exception(f"unknown character {field[row][col]} in position {row=} and {col=}!")
  
  return split_count 


# solving part 2 with a bottm-up approach b/c top-down runs in O(2^n)
def beam2(_field: list[list[str]]) -> int:

  # count the number of paths from a specific position
  def count_paths(r: int, c: int) -> int:
    # return 
    for k in range(r+1, len(_field)):
      # if we encounter a splitter, return its path count 
      if isinstance(_field[k][c], int): 
        return _field[k][c]
      elif _field[k][c] == "^":
        raise Exception(f"I missed a splitter at row={k} and col={c}!")

    # if we hit the edge there is only one path
    return 1

  # loop over all rows that can contain splitters
  for row in range(len(_field) - 2, 0, -2):
    # loop over columns in row
    for col in range(len(_field[row])):
      # if we encounter a splitter, replace it with the number of existing paths starting at its position
      if _field[row][col] == "^":
        field[row][col] = count_paths(row, col - 1) + count_paths(row, col + 1)
      
  # print final field
  for line in _field:
    print("".join([str(c) for c in line]))
      
  # return the first splitter's path count 
  for c in _field[2]:
    if isinstance(c, int):
      return c

# part 1
field = read_input()
#field = read_input("testinput.txt")
row, col = 0, field[0].index("S")
print(beam1(row, col))

# print final field
#for line in field:
#  print("".join(line))


# part 2
field = read_input()
#field = read_input("testinput.txt")
print(beam2(field))