Day01NotQuiteLisp.kt

package adventofcode.year2015

import adventofcode.Puzzle
import adventofcode.PuzzleInput

class Day01NotQuiteLisp(customInput: PuzzleInput? = null) : Puzzle(customInput) {
    override fun partOne() = input.fold(0) { floor, step -> if (step == '(') floor + 1 else floor - 1 }

    override fun partTwo() =
        input
            .mapIndexed { index, step ->
                step to input.substring(0, index + 1).fold(0) { floor, substep -> if (substep == '(') floor + 1 else floor - 1 }
            }
            .indexOfFirst { it.second == -1 }
            .plus(1)
}