class CombinationTest{
	public static void main(String[] args) {
		listCombination(new char[]{'a','b','c'});

	}
	public static void listCombination(char chs[]){
		if(chs.length == 0) return ;
		Stack<Character> stack = new Stack<Character>();
		for(int i = 1; i <= chs.length; i++){
			combine(chs, 0, i, stack);
		}
	}
	public static void combine(char []chs, int begin, int number, Stack<Character> stack){
		if(number == 0){
			System.out.println(stack.toString());
			return ;
		}
		if(begin == chs.length){
			return;
		}
		stack.push(chs[begin]);
		combine(chs, begin + 1, number - 1, stack);
		stack.pop();
		combine(chs, begin + 1, number, stack);
	}
}