string - 生成句子与变量的所有可能组合

Question

假设我有一个包含多个变量的句子，如下所示:

"lorem ipsum {a, b} dolor {c, d, e} sit amet"

假设大括号中的字母是变量，如何根据变量的所有可能组合生成一组句子？

注意:变量组的数量或变量在每组变量中的计数是未知的。

---

此特定示例的预期输出为:

"lorem ipsum {a} dolor {c} sit amet"
"lorem ipsum {b} dolor {c} sit amet"
"lorem ipsum {a} dolor {d} sit amet"
"lorem ipsum {b} dolor {d} sit amet"
"lorem ipsum {a} dolor {e} sit amet"
"lorem ipsum {b} dolor {e} sit amet"

Answer 1

在一般情况下(“变量组的数量......每组内的计数......未知”)我们应该解析初始字符串(让我们在正则表达式的帮助下完成)，然后枚举所有组合。

C#代码:

using System.Text.RegularExpressions;
...

private static IEnumerable<string> Generator(string source) {
  // parsing: variables extracted: array of variables and their possible values
  string[][] variables = Regex
    .Matches(source, @"\{.*?\}")
    .OfType<Match>()
    .Select(match => match
       .Value
       .Trim('{', '}')
       .Split(',')
       .Select(item => "{" + item.Trim() + "}")
       .ToArray())
    .ToArray();

  // now we should enumerate all possible variables' values
  int[] indexes = new int[variables.Length];

  do {
    // code golf : ugly side effects but short code
    int at = 0;

    yield return Regex.Replace(source, @"\{.*?\}", match => variables[at][indexes[at++]]);

    for (int i = 0; i < indexes.Length; ++i)
      if (indexes[i] < variables[i].Length - 1) {
        indexes[i] = indexes[i] + 1;

        break;
      }
      else
        indexes[i] = 0;
  }
  while (!indexes.All(index => index == 0));
}

演示:

string source = @"lorem ipsum {a, b} dolor {c, d, e} sit amet";

string report = string.Join(Environment.NewLine, Generator(source));

Console.Write(report);

结果:

lorem ipsum {a} dolor {c} sit amet
lorem ipsum {b} dolor {c} sit amet
lorem ipsum {a} dolor {d} sit amet
lorem ipsum {b} dolor {d} sit amet
lorem ipsum {a} dolor {e} sit amet
lorem ipsum {b} dolor {e} sit amet

另一个例子:

// 3 groups of variables with strange names
string source = @"lorem ipsum {A + 2, B, C?} dolor {XY, PQR} sit {eh?, bla-bla-bla} amet";

Console.Write(string.Join(Environment.NewLine, Generator(source)));

结果:

lorem ipsum {A + 2} dolor {XY} sit {eh?} amet
lorem ipsum {B} dolor {XY} sit {eh?} amet
lorem ipsum {C?} dolor {XY} sit {eh?} amet
lorem ipsum {A + 2} dolor {PQR} sit {eh?} amet
lorem ipsum {B} dolor {PQR} sit {eh?} amet
lorem ipsum {C?} dolor {PQR} sit {eh?} amet
lorem ipsum {A + 2} dolor {XY} sit {bla-bla-bla} amet
lorem ipsum {B} dolor {XY} sit {bla-bla-bla} amet
lorem ipsum {C?} dolor {XY} sit {bla-bla-bla} amet
lorem ipsum {A + 2} dolor {PQR} sit {bla-bla-bla} amet
lorem ipsum {B} dolor {PQR} sit {bla-bla-bla} amet
lorem ipsum {C?} dolor {PQR} sit {bla-bla-bla} amet