live enlargened grid calculation

day15/part2.lua

@@ -10,26 +10,17 @@ for line in io.lines(arg[3]) do
 	end
 	table.insert(grid, row)
 end
-
-function printgrid()
-	for r, row in pairs(grid) do
-		for c, cell in pairs(row) do
-			io.write(string.format("%3d", cell))
-		end
-		io.write('\n')
-	end
-end
-
 local h, w = #grid, #grid[1]
-for r0 = 0, 4 do
-	for c0 = 0, 4 do
-		for r = 1, h do
-			for c = 1, w do
-				local row = grid[r0*h + r] or {}
-				row[c0*w + c] = (grid[r][c] + r0 + c0 - 1) % 9 + 1
-				grid[r0*h + r] = row
-			end
-		end
+
+local function cost(r, c)
+	if r <= 0 or c <= 0 or r > 5 * h or c > 5 * w then
+		return math.huge
+	else
+		return (grid[(r-1)%h+1][(c-1)%w+1]
+		        + math.floor((r-1)/h)
+		        + math.floor((c-1)/w)
+		        - 1
+		       ) % 9 + 1
 	end
 end
 
@@ -39,22 +30,21 @@ end)
 
 local distances = {}
 
-local H = math.huge
 local n = { 1, 1, 0 }
-while n ~= nil and (distances[#grid] == nil or distances[#grid][#grid[1]] == nil) do
+while n ~= nil and (distances[5*h] == nil or distances[5*h][5*w] == nil) do
 	local r, c, d = unpack(n)
-	if 0 < r or r <= #grid or 0 < c or c <= #grid[r] then
+	if cost(r, c) < math.huge then
 		local row = distances[r] or {}
-		if d < (row[c] or H) then
+		if d < (row[c] or math.huge) then
 			row[c] = d
 			distances[r] = row
-			pq:add({ r-1, c, d + ((grid[r-1] or {})[c] or H) })
-			pq:add({ r, c-1, d + ((grid[r] or {})[c-1] or H) })
-			pq:add({ r+1, c, d + ((grid[r+1] or {})[c] or H) })
-			pq:add({ r, c+1, d + ((grid[r] or {})[c+1] or H) })
+			pq:add({ r-1, c, d + cost(r-1, c) })
+			pq:add({ r, c-1, d + cost(r, c-1) })
+			pq:add({ r+1, c, d + cost(r+1, c) })
+			pq:add({ r, c+1, d + cost(r, c+1) })
 		end
 	end
 	n = pq:pop()
 end
 
-print(distances[#grid] and distances[#grid][#grid[1]])
+print(distances[5*h] and distances[5*h][5*w])