Smalltalk

parsing logic is duplicated between the two, and I probably could use part2's logic for part 1, but yeah

part 1

day5p1: in
	| rules pages i j input |

	input := in lines.
	i := input indexOf: ''.
	rules := ((input copyFrom: 1 to: i-1) collect: [:l | (l splitOn: '|') collect: #asInteger]).
	pages := (input copyFrom: i+1 to: input size) collect: [:l | (l splitOn: ',') collect: #asInteger].
	
	^ pages sum: [ :p |
		(rules allSatisfy: [ :rule |
			i := p indexOf: (rule at: 1).
			j := p indexOf: (rule at: 2).
			(i ~= 0 & (j ~= 0)) ifTrue: [ i < j ] ifFalse: [ true ]
		])
			ifTrue: [p at: ((p size / 2) round: 0) ]
			ifFalse: [0].
	]

part 2

day5p2: in
	| rules pages i pnew input |

	input := in lines.
	i := input indexOf: ''.
	rules := ((input copyFrom: 1 to: i-1) collect: [:l | (l splitOn: '|') collect: #asInteger]).
	pages := (input copyFrom: i+1 to: input size) collect: [:l | (l splitOn: ',') collect: #asInteger].
	
	^ pages sum: [ :p |
		pnew := p sorted: [ :x :y | 
			rules anySatisfy: [ :r | (r at: 1) = x and: [ (r at: 2) = y]]
		].
		pnew ~= p
			ifTrue: [ pnew at: ((pnew size / 2) round: 0) ]
			ifFalse: [0].
	]