字符串的排列

与重复数字写法基本相同。

 public ArrayList<String> Permutation(String str) {
        ArrayList<String> list=new ArrayList<String>();
        if(str==null||str.length()==0) return list;
        char[] strnum=str.toCharArray();
        boolean[] vis=new boolean[str.length()];
        Arrays.fill(vis,false);
        StringBuilder sr=new StringBuilder();
        recure(list,strnum,vis,sr);
        return list;
    }

    public void recure(ArrayList<String> list,char[] chars,boolean[] vis,StringBuilder sr){

        if(sr.length()==chars.length) list.add(new String(sr));

        for (int i=0;i<chars.length;i++){

            if(vis[i]) continue;
            if(i>0&&chars[i]==chars[i-1]&&!vis[i-1]) continue;

            vis[i]=true;
            sr.append(chars[i]);
            recure(list,chars,vis,sr);
            vis[i]=false;
            sr.deleteCharAt(sr.length()-1);

        }
    }