创建4个字母的所有排列

问题描述：

我想创建一个由一系列4个字母组成的所有排列的数组(将4种核苷酸碱基称为A，C，G，T).程序应询问用户k的值，即排列的长度.我已经将其工作到可以得到排列的程度，但是它只显示没有重复的排列.这是程序，它现在给我的输出，以及我希望它给我的输出.

I want to create an array of all permutations of a series of 4 letters (Call them A,C,G,T for the 4 types of nucleotide bases). The program should ask the user for the value of k, the length of the permutation. I've got it working to the point where I can get the permutations, but it only shows the ones with no repeats. Here's the program, the output it's giving me right now, and the output I want it to give me.

import java.util.Arrays;
import TerminalIO.*;
public class Permute {
    static KeyboardReader reader= new KeyboardReader ();
    static int k= reader.readInt("Enter k-tuple");
    static void permute(int level, String permuted,
                        boolean[] used, String original) {

        if (level == k) {
            System.out.println(permuted);
        } else {
            for (int i = 0; i < 4; i++) {
                if (!used[i]) {
                    used[i] = true;
                    permute(level + 1, permuted + original.charAt(i), used, original);
                    used[i] = false;
                }
            }
        }
    }

    public static void main(String[] args) {
        String s = "ACGTACGTACGTACGTACGT";
        boolean used[] = new boolean[20];
        Arrays.fill(used, false);
        permute(0, "", used, s);
    }   
}

当我输入2的K值时，它会给我:

When I enter a K value of 2,it gives me:

理想情况下，它将打印:

Ideally, it would print:

答

public class Permute {

    static String s = "ACGT";

    static void permute(int level, String prefix) {

        if (level == 0) {
            System.out.println(prefix);
            return;
        }
        for (int i = 0; i < s.length(); i++)
            permute(level - 1, prefix + s.charAt(i));
    }

    public static void main(String[] args) {
        int k = 4;
        permute(k, "");
    }   

}

创建4个字母的所有排列

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