Function nQueens

kotlin/Backtracking/NQueens.kt:1–6

fun nQueens(n: Int): Int {
    // In Kotlin, Global variable is anti-pattern
    var res = mutableListOf<Int>()
    dfs(0, mutableSetOf(), mutableSetOf(), mutableSetOf(), n, res)
    return res[0]
}

fun dfs(
        r: Int,