My solution to a little Kotlin challange: https://gist.github.com/jjst/f90775efe7da80c749a140b125d6e48e

lightsout.kt

class GameState constructor (val width:Int, val height:Int, turnOnLights:List<Pair<Int, Int>>){
    var lights = BooleanArray(width * height)
    
    init {
        for(light in turnOnLights){
            toggle(light.first, light.second)
        }
    }
    
    override fun toString(): String{
        return lights.map{if(it) "x " else ". "}
        	.chunked(width)
        	.map{it + "\n"}
        	.flatten()
        	.fold("", { total, next -> total + next })
    }
    
    fun lightsOn() = lights.count{it == true}
    
    fun press(coord: Pair<Int,Int>){
        val (x, y) = coord
        toggle(x, y)
        toggle(x + 1, y)
        toggle(x - 1, y)
        toggle(x, y + 1)
        toggle(x, y - 1)
    }
    
    private fun toggle(x:Int, y:Int){
        if(x < 0 || y < 0 || x >= width || y >= height) {
            return
        }
        lights[index(x, y)] = !lights[index(x, y)]
    }
    
    private fun index(x:Int, y:Int) = y * width + x
}

fun main(args: Array<String>) {
    var game = GameState(5, 5, startingLights)
    for(move in moves) {
        game.press(move)
    }
	print(game)
    println(game.lightsOn())
}

val startingLights = listOf(
    Pair(1, 0),
    Pair(3, 0),
    Pair(1, 1),
    Pair(2, 1),
    Pair(3, 1),
    Pair(4, 1),
    Pair(0, 2),
    Pair(1, 2),
    Pair(3, 2),
    Pair(4, 2),
    Pair(0, 3),
    Pair(1, 3),
    Pair(2, 3),
    Pair(3, 3),
    Pair(4, 3),
    Pair(0, 4),
    Pair(1, 4),
    Pair(2, 4),
    Pair(3, 4),
    Pair(4, 4))

val moves = listOf(
      Pair(3, 2),
      Pair(2, 4),
      Pair(3, 3),
      Pair(0, 3),
      Pair(1, 2),
      Pair(3, 1),
      Pair(1, 4),
      Pair(4, 0),
      Pair(1, 4),
      Pair(0, 1),
      Pair(0, 1),
      Pair(0, 2),
      Pair(0, 2),
      Pair(3, 1),
      Pair(0, 4),
      Pair(2, 2),
      Pair(1, 3),
      Pair(3, 1),
      Pair(2, 2),
      Pair(1, 1),
      Pair(0, 0),
      Pair(4, 3),
      Pair(4, 4),
      Pair(2, 3),
      Pair(4, 3))