Question

嗨，我有一个关于递归算法的问题。这段代码运行时间过长。我已经从Internet上搜索了，我计划将算法从递归改为迭代。

我很难更改代码，因为没有“返回”条件（它总是循环直到年份，类型，操作，位置，部门和职位列表完成）。

如何更改算法？

以下是代码：

DataSet dataSet = new DataSet();
var years = GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { string.Empty }, group);
foreach (var year in years)
{
   var types = GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { year.Year.ToString() }, group);
   foreach (var type in types)
   {
      var departments = GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { year.Year.ToString(), type.ContractorType }, group);
      foreach (var department in departments)
      {
          var operations = GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { year.Year.ToString(), type.ContractorType, department.Department }, group);
          foreach (var operation in operations)
          {
             var positions = GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { year.Year.ToString(), type.ContractorType, department.Department, operation.Operation }, group);
             foreach (var position in positions)
             {
                 var locations = GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { year.Year.ToString(), type.ContractorType, department.Department, operation.Operation, position.Position }, group);
                 foreach (var location in locations)
                 {
                    DataTable tbl = ReportExport.ConvertToDataTable<ReportMonthlyFTE>(
                                   GetDataForReportMonthlyFTEWorkCompletionByDepartment(new string[] { year.Year.ToString(), type.ContractorType, department.Department, operation.Operation, position.Position, location.Location }, group).ToList());
                                    dataSet.Tables.Add(tbl);
                 }
             }
         }
      }
   }
}

Answer 1

我认为yield可能会解决您的问题。这将允许您从调用代码控制枚举，以便您可以在需要时提前逃脱。

class Program
{
    static void Main(string[] args)
    {
        foreach (var dataTable in GetData())
        {
            Console.WriteLine("Got more data.");

            Console.WriteLine("Continue getting more data?");
            ConsoleKeyInfo keyInfo = Console.ReadKey();

            if (keyInfo.KeyChar != 'y')
            { 
                // Stop enumerating.
                break; 
            }
        }

        Console.ReadKey(true);
    }

    static IEnumerable<DataTable> GetData()
    {
        while (true)
        {
            yield return new DataTable();
        }
    }
}

另请注意返回类型IEnumerable<out T>。

将递归算法转换为迭代算法

1 个答案: