數(shù)據(jù)結(jié)構(gòu)與算法分析的課后習(xí)題編寫帶有下列聲明的例程：public void permute( String str );private void permute( char [] str, int low, int high );第一個(gè)例程是驅(qū)動(dòng)程序，它調(diào)用第二個(gè)例程并顯示String str中的字符的所有排列。如果str是"abc",那么輸出的串則是abc,acb,bac,bca,cab和cba。第二個(gè)例程使用遞歸。答案如下：public class Permute{public void permute ( String str ){    permute (str.toCharArray (), 0, str.length ());    String tmp = new StringBuilder ().append (str).reverse ().toString ();    permute (tmp.toCharArray (), 0, tmp.length ());}private void permute ( char[] str, int low, int high ){    if (low == high)    {        return;    }    String result = "";    for ( int i = low; i < high; i++ )    {        result += str[i];    }    if (result.length () < str.length)    {        int count = str.length - result.length ();        for ( int i = 0; i < count; i++ )        {            result += str[i];        }    }    System.out.println (result);    permute (str, ++low, high);}public static void main ( String[] args ){    Permute permute = new Permute ();    permute.permute ("abc");}}上面的代碼，雖然也是方法自己調(diào)用自身，但感覺permute (str, ++low, high);這樣的調(diào)用其實(shí)用for循環(huán)就能寫出來(lái)，這個(gè)應(yīng)該不能算是遞歸吧，求更好的遞歸解法