Question

我正在编写一个程序来列出字符串的所有子集。我的程序（下面给出）按顺序列出了“abcd”的子集：

'' 'd' 'c' 'cd' 'b' 'bd' 'bc' 'bcd' 'a' 'ad' 'ac' 'acd' 'ab' 'abd' 'abc' 'abcd'

哪个是对的。但是，参考解决方案按以下顺序列出：

'' 'a' 'b' 'ab' 'c' 'ac' 'bc' 'abc' 'd' 'ad' 'bd' 'abd' 'cd' 'acd' 'bcd' 'abcd'

我的问题是：这个订单的名称是什么？

供参考，这是我的程序：

import java.util.ArrayList;
import java.util.Collections;

/**
   This class generates subsets of a string.
*/
public class SubsetGenerator
{
   public static ArrayList<String> getSubsets(String word)
   {
       ArrayList<String> result = new ArrayList<String>();
      //fill out
       //result.add("");
       if(word.length() == 0)
       {

           result.add("");
        }

   else
    {
        String notFirst = word.substring(1);
        ArrayList<String> smaller = getSubsets(notFirst);
        //System.out.println(smaller);
        char first = word.charAt(0);

        result.addAll(smaller);

        for(String i: smaller)
        {
            result.add(first+i);
        }
    }


   //simpleSubsets = getSubsets(simple+word.charAt(0));

  // Form a simpler word by removing the first character
  // fill out

  // Generate all subsets of the simpler word
  // fill out

  // Add the removed character to the front of
  // each subset of the simpler word, and
  // also include the word without the removed character
  // fill out

  // Return all subsets
  return result;
   }
}

Answer 1

他们生成的顺序是您在二进制数中计算并将数字0和1转换为a，b，c和d时所获得的顺序：

d c b a | set
--------+----
0 0 0 0 | {}
0 0 0 1 | {a}
0 0 1 0 | {b}
0 0 1 1 | {a, b}
0 1 0 0 | {c}
0 1 0 1 | {a, c}
0 1 1 0 | {b, c}
0 1 1 1 | {a, b, c}
1 0 0 0 | {d}
1 0 0 1 | {a, d}
1 0 1 0 | {b, d}
1 0 1 1 | {a, b, d}
1 1 0 0 | {c, d}
1 1 0 1 | {a, c, d}
1 1 1 0 | {b, c, d}
1 1 1 1 | {a, b, c, d}

希望这有帮助！

这些子集的列表顺序是什么？

1 个答案: