正则表达式的问题

Question

几个不同的字母的随意组合都匹配，但是一旦出现某几个字母重复就不匹配，该怎么写？
即：
能够匹配abcd,AbDc,daCb等等，
但不匹配aabc,Dccb,abca

Answer 1

public class Example12{
        public static void main(String args[]) {
            int i,j,k,n;
            String[] s = {"a","b","c","d"};
            for(i=1;i<5;i++){
                for(j=1;j<5;j++){
                    for(k=1;k<5;k++){
                        if (i!=j && i!=k && j!=k){
                            System.out.println(s[i-1] + ", " + s[j-1] + ", " + s[k-1]);
                        }
                    }
                }
            }
           
        }
}

Answer 2

public class Test{
        public static void main(String args[]) {
            int i,j,k,n;
            String[] s = {"a","b","c","d"};
            for(i=1;i<5;i++){
                for(j=1;j<5;j++){
                    for(k=1;k<5;k++){
                        if (i!=j && i!=k && j!=k){
                            System.out.println(s[i-1] + ", " + s[j-1] + ", " + s[k-1]);
                        }
                    }
                }
            }
           
        }
}