Java面试题：输出字符串的所有组合

问题描述：假设字符串中所有的字符都不重复，输出字符串中的所有组合！

public class StringTestDemo {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub

String s="abc";
char[] c=s.toCharArray();
// StringBuffer sb=new StringBuffer("");
// int len=c.length;
// for (int i = 0; i <= len; i++) {
// CombineRecursiveImpl(c,0,i,sb);
// }

Combine(c);
}

private static void CombineRecursiveImpl(char[] c, int begin, int len,
StringBuffer sb) {
// TODO Auto-generated method stub
if(len==0){
System.out.println(sb+" ");
return;
}
if(begin==c.length){
return;
}
sb.append(c[begin]);
CombineRecursiveImpl(c,begin+1,len-1,sb);
sb.deleteCharAt(sb.length()-1);
CombineRecursiveImpl(c,begin+1,len,sb);
}

public static void Combine(char[] c){
if(c==null){
return;
}
int len=c.length;
boolean used[]=new boolean[len];
char cache[]=new char[len];

int result=len;

while(true){
int index=0;
while(used[index]){
used[index]=false;
++result;
if(++index==len){
return;
}
}

used[index]=true;
cache[--result]=c[index];
System.out.println(new String(cache).substring(result)+" ");
}
}

}