Question

我有以下代码将生成输入字符串的排列，但是是否可以更改它以便不使用for循环，只是递归？

public static void findPermutations (String beginningString, String endingString) {
    if (endingString.length() <= 1)
      System.out.println(beginningString + endingString);
    else
      for (int i = 0; i < endingString.length(); i++) {
        try {
          String newString = endingString.substring(0, i) + endingString.substring(i + 1);

          permuteString(beginningString + endingString.charAt(i), newString);
        } catch (StringIndexOutOfBoundsException exception) {
          exception.printStackTrace();
        }
      }
}

Answer 1

这是我在其他地方找到的答案，所以对我没有任何好处。

虽然无法再找到问题

public class Permutations {

    // print N! permutation of the characters of the string s (in order)
    public  static void perm1(String s) { perm1("", s); }
    private static void perm1(String prefix, String s) 
    {
        int N = s.length();
        if (N == 0)
        {
            System.out.println(prefix);
        }
        else {
            for (int i = 0; i < N; i++)
               perm1(prefix + s.charAt(i), s.substring(0, i) + s.substring(i+1, N));
        }

    }

    // print N! permutation of the elements of array a (not in order)
    public static void perm2(String s) {
        int N = s.length();
        char[] a = new char[N];
        for (int i = 0; i < N; i++)
            a[i] = s.charAt(i);
        perm2(a, N);
    }

    private static void perm2(char[] a, int n) {
        if (n == 1) {
            if(new String(a).contains("ncl-"))
                System.out.println(a);
            return;
        }
        for (int i = 0; i < n; i++) {
            swap(a, i, n-1);
            perm2(a, n-1);
            swap(a, i, n-1);
        }
    }  

    // swap the characters at indices i and j
    private static void swap(char[] a, int i, int j) {
        char c = a[i];
        a[i] = a[j];
        a[j] = c;
    }



    public static void main(String[] args) throws IOException {
        //String word = "nst n-eitoira cp2vmamoocnla1e k nfto-k7re id6";
        String word = "doggy";
        perm1(word);
        System.out.println();
        perm2(word);
    }
}

Java：另一种产生排列的方法？

1 个答案: