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The Lantern Festival solution in Clear category for The Lantern Festival by vinc
from itertools import product
DIRS = {'S': (1, 0), 'N': (-1, 0), 'E': (0, 1), 'W': (0, -1)}
class Lantern:
def __init__(self, river, cell):
self.river = river
self.cell = cell
self.track = [cell]
def make_track(self, start, direction):
""" write track for the lantern using right-hand rule """
row, col = start
d = direction
while row < self.river.finish:
d_row, d_col = DIRS[d]
f_cell = (row + d_row, col + d_col) # forward
r_cell = (row + d_col, col - d_row) # right
l_cell = (row - d_col, col + d_row) # left
clean_water = list(filter(self.river.is_clean_water,
(f_cell, r_cell, l_cell)))
if not clean_water:
return
elif len(clean_water) == 1:
next_cell = clean_water[0]
else:
next_cell = r_cell if r_cell in clean_water else f_cell
self.track.append(next_cell)
# find direction for next_cell and repeat loop
for d in DIRS:
if (row + DIRS[d][0], col + DIRS[d][1]) == next_cell:
row, col = next_cell
break
def move(self, step):
""" set lantern at track's position """
if step < len(self.track):
self.cell = self.track[step]
else:
self.cell = self.track[-1]
def lightened_water(self):
""" return set of lightened water cells by the lantern """
row, col = self.cell
return set(filter(self.river.is_water, product((row+1, row, row-1),
(col+1, col, col-1))))
class River:
def __init__(self, river_map):
self.map = river_map
self.finish = len(river_map)-1
self.lanterns = [Lantern(self, (0,i)) for i,s in enumerate(river_map[0])
if s == '.']
self.passed = set()
for lantern in self.lanterns:
lantern.make_track(lantern.cell, 'S')
self.passed.update(lantern.track)
def flow(self, step):
""" set all lanterns at their tracks positions """
for lantern in self.lanterns:
lantern.move(step)
def lightened_water(self):
""" return set of lightened water cells """
cells = set()
for lantern in self.lanterns:
cells.update(lantern.lightened_water())
return cells
def is_water(self, cell):
""" return True if water is at cell """
row,col = cell
return (0 <= row < len(self.map) and 0 <= col < len(self.map[0]) and
self.map[row][col] == '.')
def is_clean_water(self, cell):
""" return True if cell available for move """
return self.is_water(cell) and cell not in self.passed
def print_map(self):
""" print map with lanterns on it """
lanterns_on_map = list(self.map)
for i,lantern in enumerate(self.lanterns):
row,col = lantern.cell
lanterns_on_map[row] = lanterns_on_map[row][:col] + str(i) + lanterns_on_map[row][col+1:]
for row in lanterns_on_map:
print(row)
def lanterns_flow(river_map, minutes):
river = River(river_map)
river.flow(minutes)
return len(river.lightened_water())
Aug. 19, 2014
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