solve day 16 part 2

1 files changed, 111 insertions, 0 deletions

diff --git a/16/2.lua b/16/2.lua
new file mode 100644
index 0000000..996d186
--- /dev/null
+++ b/16/2.lua
@@ -0,0 +1,111 @@
+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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