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@@ -0,0 +1,111 @@
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+function read_matrix(filename)
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+ local fp = io.open(filename, 'r')
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+ local lines = {}
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+ while true do
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+ local line = fp:read()
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+ if (not line) or #line == 0 then break end
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+ table.insert(lines, line)
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+ end
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+ return lines
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+end
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+
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+local layout = read_matrix('input')
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+local height = #layout
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+local width = #layout[1]
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+
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+local count_actived = function(layout, x, y, direction)
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+ local trace_set = {}
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+ local active_set = {}
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+ local count = 0
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+
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+ local trace
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+ trace = function (layout, x, y, direction)
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+ if x < 1 or x > width then return nil end
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+ if y < 1 or y > width then return nil end
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+
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+ trace_key = x..','..y..','..direction
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+ if trace_set[trace_key] == nil then
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+ trace_set[trace_key] = 1
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+ else
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+ return nil
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+ end
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+
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+ if active_set[x..','..y] == nil then
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+ active_set[x..','..y] = 1
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+ count = count + 1
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+ end
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+ -- trace next
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+ local cur = layout[y]:sub(x,x)
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+ if cur == '.' then
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+ if direction == 'E' then
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+ trace(layout, x+1, y, direction)
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+ elseif direction == 'W' then
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+ trace(layout, x-1, y, direction)
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+ elseif direction == 'N' then
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+ trace(layout, x, y-1, direction)
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+ elseif direction == 'S' then
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+ trace(layout, x, y+1, direction)
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+ end
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+ elseif cur == '-' then
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+ if direction == 'E' then
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+ trace(layout, x+1, y, direction)
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+ elseif direction == 'W' then
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+ trace(layout, x-1, y, direction)
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+ elseif direction == 'N' or direction == 'S' then
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+ trace(layout, x+1, y, 'E')
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+ trace(layout, x-1, y, 'W')
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+ end
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+ elseif cur == '|' then
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+ if direction == 'E' or direction == 'W' then
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+ trace(layout, x, y-1, 'N')
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+ trace(layout, x, y+1, 'S')
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+ elseif direction == 'N' then
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+ trace(layout, x, y-1, direction)
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+ elseif direction == 'S' then
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+ trace(layout, x, y+1, direction)
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+ end
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+ elseif cur == '/' then
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+ if direction == 'E' then
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+ trace(layout, x, y-1, 'N')
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+ elseif direction == 'W' then
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+ trace(layout, x, y+1, 'S')
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+ elseif direction == 'N' then
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+ trace(layout, x+1, y, 'E')
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+ elseif direction == 'S' then
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+ trace(layout, x-1, y, 'W')
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+ end
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+ elseif cur == '\\' then
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+ if direction == 'E' then
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+ trace(layout, x, y+1, 'S')
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+ elseif direction == 'W' then
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+ trace(layout, x, y-1, 'N')
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+ elseif direction == 'N' then
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+ trace(layout, x-1, y, 'W')
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+ elseif direction == 'S' then
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+ trace(layout, x+1, y, 'E')
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+ end
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+ end
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+ end
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+
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+ trace(layout, x, y, direction)
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+ return count
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+end
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+
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+
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+local max = -1
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+
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+for i = 1,height do
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+ local count1 = count_actived(layout, 1, i, 'E')
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+ if count1 > max then max = count1 end
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+ local count2 = count_actived(layout, width, i, 'W')
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+ if count2 > max then max = count2 end
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+end
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+
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+for i = 1,width do
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+ local count1 = count_actived(layout, i, 1, 'S')
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+ if count1 > max then max = count1 end
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+ local count2 = count_actived(layout, i, height, 'N')
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+ if count2 > max then max = count2 end
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+end
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+
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+print(max)
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