输入字符串"abc",输出组合a,b,c,ab,ac,bc,abc
class Main {
public static void main(String[] args){
String s = new Scanner(System.in).next();
combine(s);
}
public static void combine(String str){
char[] in=str.toCharArray();
StringBuilder out = new StringBuilder();
List<String> list = new ArrayList<>();
allCombine(in,out,0,list);
list.stream().forEach(s -> System.out.print(s+" "));
}
public static void allCombine(char[] ch, StringBuilder sb, int start, List<String> list){
int len=ch.length-1;
for(int i=start;i<=len;i++){
sb.append(ch[i]);
list.add(sb+"");
Collections.sort(list,(o1, o2) -> o1.length() - o2.length());
if(i<len){
allCombine(ch,sb,i+1,list);
}
sb.setLength(sb.length()-1);
}
}
}