inital commitHEADmaster

1 files changed, 48 insertions, 0 deletions

diff --git a/09/1.lua b/09/1.lua
new file mode 100644
index 0000000..8757767
--- /dev/null
+++ b/09/1.lua
@@ -0,0 +1,48 @@
+local knots, tail_moved = {}, {}
+for i = 1,10 do table.insert(knots,{1,1}) end
+local directions = {
+	R = {1,0},
+	U = {0,1},
+	L = {-1,0},
+	D = {0,-1},
+}
+local sfmt = "%d - %d"
+local motion = {}
+for i = -2,2 do
+	for j = -2, 2 do
+		if math.abs(i)^2 + math.abs(j)^2 > 2 then
+			motion[sfmt:format(i,j)] = {
+				i == 0 and 0 or math.abs(i)/i,
+				j == 0 and 0 or math.abs(j)/j
+			}
+		else
+			motion[sfmt:format(i,j)] = {0,0}
+		end
+	end
+end
+local function insert_tail_pos()
+	local tail = knots[#knots]
+	tail_moved[string.format(sfmt,tail[1],tail[2])] = true
+end
+local function move_knot(knot,twords)
+	local x,y = twords[1] - knot[1], twords[2] - knot[2]
+	local direction = motion[string.format("%d - %d",x,y)]
+	knot[1],knot[2] = knot[1] + direction[1], knot[2] + direction[2]
+end
+insert_tail_pos()
+for line in io.lines() do
+	local direction, steps = line:match("([RULD]) (%d+)")
+	direction = directions[direction]
+	for i = 1,steps do
+		knots[1][1], knots[1][2] = knots[1][1] + direction[1], knots[1][2] + direction[2]
+		for j = 2,#knots do
+			move_knot(knots[j],knots[j-1])
+			insert_tail_pos()
+		end
+	end
+end
+local tmr = {}
+for p,_ in pairs(tail_moved) do
+	table.insert(tmr,p)
+end
+print(#tmr)