Nim
I've got my first sub-1000 rank today (998 for part 2). Yay!
Simple and straightforward challenge, very fitting for 1st day. Gonna enjoy it while it lasts.
proc solve(input: string): AOCSolution[int, int] =
var l1,l2: seq[int]
for line in input.splitLines():
let pair = line.splitWhitespace()
l1.add parseInt(pair[0])
l2.add parseInt(pair[1])
l1.sort()
l2.sort()
block p1:
for i in 0..l1.high:
result.part1 += abs(l1[i] - l2[i])
block p2:
for n in l1:
result.part2 += n * l2.count(n)