Coding challenge

AddsToAHundred.groovy

class AddsToAHundred {
	/*
		Challenge: Write a program that outputs all possibilities
		to put + or - or nothing between the numbers 1, 2, ..., 9 (in this order)
		such that the result is always 100. For example: 1 + 2 + 34 – 5 + 67 – 8 + 9 = 100.
		
		from https://blog.svpino.com/2015/05/07/five-programming-problems-every-software-engineer-should-be-able-to-solve-in-less-than-1-hour
	*/

        public static void main(String [] args) {
                explore([])
        }   

        static def explore(commandsSoFar) {
                if(commandsSoFar.size() == 8) {
                        return testIfAHundred(commandsSoFar)
                }   
                else {
                        explore(commandsSoFar + '') 
                        explore(commandsSoFar + '+')
                        explore(commandsSoFar + '-')
                }   
        }   

        static def testIfAHundred(list) {
                def input = []
                def accumulator = 0 
                8.times {
                        input << (it + 1)
                        input << list[it]
                }   
                input << '9' 
                def command = input.join('')
                command.split('\\+').each { addOperand ->
                        addOperand.split('-').eachWithIndex { subOperand, index ->
                                accumulator += ((index == 0) ? 1 : -1) * Integer.parseInt(subOperand)
                        }   
                }   
                if(accumulator == 100) {
                        println command
                        return true
                }   
        }   
}