Solution

fun find(numbers: IntArray, index: Int = 0, data: String = "") {
    if (index >= numbers.size) {
        if (data.isNotEmpty() && eval(data).compareTo(Result) == 0)
            println("$data = $Result")
    } else {
        val number = numbers[index].toString()
        if (index == 0) {
            find(numbers, 1, number)
            find(numbers, 1, Minus + number)
        } else
            for (operator in Operators)
                find(numbers, index + 1, data + operator + number)
    }
}

fun eval(data: String) = Expression(data).eval()

val Numbers = intArrayOf(6, 6, 1, 3, 7, 6, 6)
val Result = BigDecimal("100")
val Operators = arrayOf("+", "-", "/", "*")
val Minus = "-"