ab的排列 aa , ab ba,bb

package reverseList;

public class Main {
    static void perm(char c[],int lev,char ans[])
    {
        if(c.length==lev)
        {
            System.out.println(String.valueOf(ans));
        }
        else
        {
        for(int i=0;i<c.length;i++)
        {
            ans[lev]=c[i];
            perm(c,lev+1,ans);

        }
        }

    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        char c[]="ab".toCharArray();
        char ans[]=new char[3];
        perm(c,0,ans);

    }

}