2020 day 12

2020/12/day12.lua

@@ -0,0 +1,64 @@
+local parsed = {}
+for line in io.lines() do
+    table.insert(parsed, {line:sub(1, 1), tonumber(line:sub(2))})
+end
+
+-- Ship/waypoint position and direction
+local e, n, dir_e, dir_n = 0, 0, 1, 0
+
+-- Rotates the ship clockwise.
+local function rotate_part1(value)
+    for _ = 1, value / 90 do
+        if dir_e == 0 then
+            -- Switching from North to East or South to West
+            dir_n, dir_e = dir_e, dir_n
+        else
+            -- Switching from East to South or West to North
+            dir_n, dir_e = -dir_e, 0
+        end
+    end
+end
+
+local functions = {
+    N=function (value) n = n + value end,
+    S=function (value) n = n - value end,
+    E=function (value) e = e + value end,
+    W=function (value) e = e - value end,
+    F=function (value) e, n = e + dir_e * value, n + dir_n * value end,
+    R=rotate_part1,
+    L=function (value) rotate_part1(360-value) end
+}
+
+local function run()
+    for _, instruction in ipairs(parsed) do
+        functions[instruction[1]](instruction[2])
+    end
+    return math.abs(e) + math.abs(n)
+end
+
+print(run())
+
+--[[
+    Update the functions and state for part 2
+    Here, dir_ variables are the waypoint itself.
+    NSEW change the waypoint instead of moving the ship.
+--]]
+e, n, dir_e, dir_n = 0, 0, 10, 1
+
+-- Rotate the waypoint around the ship clockwise.
+local function rotate_part2(value)
+    for _ = 1, value / 90 do
+        dir_n, dir_e = -dir_e, dir_n
+    end
+end
+
+functions = {
+    N=function (value) dir_n = dir_n + value end,
+    S=function (value) dir_n = dir_n - value end,
+    E=function (value) dir_e = dir_e + value end,
+    W=function (value) dir_e = dir_e - value end,
+    F=function (value) e, n = e + dir_e * value, n + dir_n * value end,
+    R=rotate_part2,
+    L=function (value) rotate_part2(360-value) end
+}
+print(run())

README.md

@@ -22,7 +22,7 @@ is acceptable; anything goes as long as I solve it myself!
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