Day 1

.gitignore

@@ -1,3 +1,5 @@
+input/
+
 # ---> Lua
 # Compiled Lua sources
 luac.out

1.lua

@@ -0,0 +1,32 @@
+#!/bin/env lua
+
+local left, right = {}, {}
+local rightCount = {}
+for line in assert(io.open("input/1")):lines() do
+	local l, r = line:match("(%d+)%s+(%d+)")
+	l, r = assert(tonumber(l)), assert(tonumber(r))
+
+	table.insert(left, l)
+	table.insert(right, r)
+
+	rightCount[r] = (rightCount[r] or 0) + 1
+end
+
+table.sort(left)
+table.sort(right)
+
+local sumDiff = 0
+for i=1,#left do
+	local diff = math.abs(left[i] - right[i])
+	sumDiff = sumDiff + diff
+end
+
+print("Part one", sumDiff)
+
+local simScore = 0
+for _,l in ipairs(left) do
+	simScore = simScore + l * (rightCount[l] or 0)
+end
+
+print("Part two", simScore)
+