120 lines
3.3 KiB
Python
120 lines
3.3 KiB
Python
from helpers import *
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lines = read_day(24).split('\n')[1:-1] # strip walls
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sample_lines = '''
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#.######
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#>>.<^<#
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#.<..<<#
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#>v.><>#
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#<^v^^>#
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######.#'''.strip().split('\n')[1:-1]
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def sim(lines):
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height = len(lines)
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width = len(lines[0]) - 2
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blizzards_left = set()
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blizzards_right = set()
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blizzards_up = set()
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blizzards_down = set()
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for row, line in enumerate(lines):
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for col, c in enumerate(line[1:-1]): # strip walls
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if c == '<':
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blizzards_left.add((col, row))
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elif c == '>':
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blizzards_right.add((col, row))
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elif c == '^':
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blizzards_up.add((col, row))
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elif c == 'v':
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blizzards_down.add((col, row))
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def position_free(col: int, row: int, time: int) -> bool:
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if ((col+time)%width, row) in blizzards_left:
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return False
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if ((col-time)%width, row) in blizzards_right:
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return False
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if (col, (row+time)%height) in blizzards_up:
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return False
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if (col, (row-time)%height) in blizzards_down:
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return False
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return True
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seen_states = set()
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state_stack = [(0,-1,0)]
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def try_add_state(col: int, row: int, time: int):
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if col < 0 or col >= width or row < -1 or row > height:
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return
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if row == -1 and col != 0:
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return
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if row == height and col != width-1:
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return
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if not position_free(col, row, time):
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return
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triple = (col, row, time)
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if triple not in seen_states:
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seen_states.add(triple)
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state_stack.append(triple)
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best_time = 1000
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goal = (width-1, height) # End position
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print('Moving from start to end')
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while state_stack:
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col, row, t = state_stack.pop()
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t1 = t + 1
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goal_distance = abs(goal[0]-col) + abs(goal[1]-row) # Manhattan distance
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if goal_distance == 1: # we're right next to the goal! move there and end this trail
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best_time = min(best_time, t1)
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continue
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if t + goal_distance > best_time:
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continue
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try_add_state(col-1, row, t1)
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try_add_state(col, row-1, t1)
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try_add_state(col, row, t1)
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try_add_state(col+1, row, t1)
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try_add_state(col, row+1, t1)
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p1 = best_time
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state_stack = [(width-1, height, best_time)]
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seen_states.clear()
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best_time = 10_000
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goal = (0, -1) # Starting position
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print('Moving from end to start')
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while state_stack:
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col, row, t = state_stack.pop()
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t1 = t + 1
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goal_distance = abs(goal[0]-col) + abs(goal[1]-row) # Manhattan distance
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if goal_distance == 1: # we're right next to the goal! move there and end this trail
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best_time = min(best_time, t1)
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continue
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if t + goal_distance > best_time:
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continue
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try_add_state(col+1, row, t1)
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try_add_state(col, row+1, t1)
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try_add_state(col, row, t1)
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try_add_state(col-1, row, t1)
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try_add_state(col, row-1, t1)
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state_stack = [(0,-1,best_time)]
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seen_states.clear()
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best_time = 100_000
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goal = (width-1, height) # End position
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print('Moving from start to end (2)')
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while state_stack:
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col, row, t = state_stack.pop()
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t1 = t + 1
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goal_distance = abs(goal[0]-col) + abs(goal[1]-row) # Manhattan distance
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if goal_distance == 1: # we're right next to the goal! move there and end this trail
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best_time = min(best_time, t1)
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continue
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if t + goal_distance > best_time:
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continue
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try_add_state(col-1, row, t1)
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try_add_state(col, row-1, t1)
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try_add_state(col, row, t1)
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try_add_state(col+1, row, t1)
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try_add_state(col, row+1, t1)
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return p1, best_time
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print(sim(sample_lines))
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print(sim(lines))
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