输入字符串“abc“，输出组合a,b,c,ab,ac,bc,abc

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<>();//将组合添加至list中，排序。按照a,b,c,ab,ac,abc输出 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]); //System.out.print(sb+" "); =>不添加至list中，直接打印 a,ab,abc,abcd,ac,acd,b,bc,bd,d 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);//执行完abcd后，回溯 -> abc -> ab重新执行 abd } } }