深搜系列之字符串全组合

import java.util.ArrayList;

public class FullCombination {

    public static void main(String[] args) {
        ArrayList<String> result = new ArrayList<>();
        helper(result, "abc", new StringBuilder(), 0);
        for (String s : result)
            System.out.println(s);
    }

    private static void helper(ArrayList<String> result, String s, StringBuilder sb, int index) {

        for (int i = index; i < s.length(); i++) {
            sb.append(s.charAt(i));
            result.add(sb.toString());
            helper(result, s, sb, i + 1);
            sb.deleteCharAt(sb.length() - 1);
        }

    }
}