advent_day_1.swift

// http://adventofcode.com/day/1 - part 1
//
// instructions - String containing coded instructions for moving up a floor with
// "(" and down a floor with ")"
// Starting ground floor numbered zero is assumed.
// Returns an integer value for the expected floor.
func upsAndDowns(instructions: String) -> Int {
    var floor: Int = 0

    for character in instructions.characters {
        if character == "(" {
            floor += 1
        } else if character == ")" {
            floor -= 1
        }
    }

    return floor
}


// http://adventofcode.com/day/1 - part 2
//
// instructions - String containing coded instructions for moving up a floor with
// "(" and down a floor with ")"
// Starting ground floor numbered zero is assumed.
// Also assuming that the first character of the instructions is considered
// instruction #1 (not zero).
//
// Returns an integer value for the first instruction that leads to the basement
// (floor -1), or nil if it did not ever lead there.
func inTheBasement(instructions: String) -> Int? {
    var floor: Int = 0

    for (index, character) in instructions.characters.enumerate() {
        if character == "(" {
            floor += 1
        } else if character == ")" {
            floor -= 1
        }

        if floor == -1 {
            return index + 1
        }
    }

    return nil
}