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function read_matrix(filename)
local fp = io.open(filename, 'r')
local lines = {}
while true do
local line = fp:read()
if (not line) or #line == 0 then break end
table.insert(lines, line)
end
return lines
end
local layout = read_matrix('input')
local height = #layout
local width = #layout[1]
local count_actived = function(layout, x, y, direction)
local trace_set = {}
local active_set = {}
local count = 0
local trace
trace = function (layout, x, y, direction)
if x < 1 or x > width then return nil end
if y < 1 or y > width then return nil end
trace_key = x..','..y..','..direction
if trace_set[trace_key] == nil then
trace_set[trace_key] = 1
else
return nil
end
if active_set[x..','..y] == nil then
active_set[x..','..y] = 1
count = count + 1
end
-- trace next
local cur = layout[y]:sub(x,x)
if cur == '.' then
if direction == 'E' then
trace(layout, x+1, y, direction)
elseif direction == 'W' then
trace(layout, x-1, y, direction)
elseif direction == 'N' then
trace(layout, x, y-1, direction)
elseif direction == 'S' then
trace(layout, x, y+1, direction)
end
elseif cur == '-' then
if direction == 'E' then
trace(layout, x+1, y, direction)
elseif direction == 'W' then
trace(layout, x-1, y, direction)
elseif direction == 'N' or direction == 'S' then
trace(layout, x+1, y, 'E')
trace(layout, x-1, y, 'W')
end
elseif cur == '|' then
if direction == 'E' or direction == 'W' then
trace(layout, x, y-1, 'N')
trace(layout, x, y+1, 'S')
elseif direction == 'N' then
trace(layout, x, y-1, direction)
elseif direction == 'S' then
trace(layout, x, y+1, direction)
end
elseif cur == '/' then
if direction == 'E' then
trace(layout, x, y-1, 'N')
elseif direction == 'W' then
trace(layout, x, y+1, 'S')
elseif direction == 'N' then
trace(layout, x+1, y, 'E')
elseif direction == 'S' then
trace(layout, x-1, y, 'W')
end
elseif cur == '\\' then
if direction == 'E' then
trace(layout, x, y+1, 'S')
elseif direction == 'W' then
trace(layout, x, y-1, 'N')
elseif direction == 'N' then
trace(layout, x-1, y, 'W')
elseif direction == 'S' then
trace(layout, x+1, y, 'E')
end
end
end
trace(layout, x, y, direction)
return count
end
local max = -1
for i = 1,height do
local count1 = count_actived(layout, 1, i, 'E')
if count1 > max then max = count1 end
local count2 = count_actived(layout, width, i, 'W')
if count2 > max then max = count2 end
end
for i = 1,width do
local count1 = count_actived(layout, i, 1, 'S')
if count1 > max then max = count1 end
local count2 = count_actived(layout, i, height, 'N')
if count2 > max then max = count2 end
end
print(max)
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