手動終止遞歸

Question

我寫了一個遞歸（實際上我找到了遞歸在線）來獲取一組數字的所有可能的排列，但在某些情況下，由於大量的可能排列，我想添加一個If語句在經歷所有排列之前終止遞歸。我試過輸入一個return語句，但它似乎不起作用。

我在編碼方面有點新手，所以如果答案對每個人都是顯而易見的，我就是無法得到它。

class EntryPoint 
{   
    static void Main() 
    {   
     //input an initial sequence of the trains to schedule 
     Console.Write("Input train permutation"); 
     string inputLine = Console.ReadLine(); 

     GenerateTrainOrder GTO = new GenerateTrainOrder(); 
     GTO.InputSet = GTO.MakeCharArray(inputLine); 
     GTO.CalcPermutation(0); 
    } 
} 


class GenerateTrainOrder 
{ 
    private int elementLevel = -1; // elements examined iterates immediately after the CalcPermutation initiates so we must set it equal -1 to start from 0 
    private int[] permutationValue = new int[0]; 

    public int[,] Paths = new int[ParametersClass.timetableNumber, ParametersClass.trainsToSchedule]; 

    private char[] inputSet; 
    public char[] InputSet 
    { 
     get { return inputSet; } 
     set { inputSet = value; } 
    } 

    private int permutationCount = 0; 
    public int PermutationCount 
    { 
     get { return permutationCount; } 
     set { permutationCount = value; } 
    } 

    //transform the input from the console to an array for later use 
    public char[] MakeCharArray(string InputString) 
    { 
     char[] charString = InputString.ToCharArray(); 
     Array.Resize(ref permutationValue, charString.Length); 

     return charString; 
    } 

    public void CalcPermutation(int k) 
    {    
      elementLevel++; 
      permutationValue.SetValue(elementLevel, k); 

      //if we have gone through all the elements which exist in the set, output the results 
      if (elementLevel == ParametersClass.trainsToSchedule) 
      { 
       OutputPermutation(permutationValue); // output TrainOrder by passing the array with the permutation 
      } 

      //if there are elements which have not been allocated a place yet 
      else 
      { 
       for (int i = 0; i < ParametersClass.trainsToSchedule; i++) 
       { 
        //iterate until we come upon a slot in the array which has not been allocated an elements yet 
        if (permutationValue[i] == 0) 
        { 

         CalcPermutation(i); //rerun the code to allocate an element to the empty slot. the location of the empty slot is given as a parameter (this is how k increments) 

        } 
       } 
      } 

      elementLevel--; 
      permutationValue.SetValue(0, k); 
    } 

    private void OutputPermutation(int[] value) 
    { 
     int slot = 0; 

     foreach (int i in value) 
     { 
      Paths[permutationCount, slot] = Convert.ToInt16(Convert.ToString(inputSet.GetValue(i-1))); 

      slot++; 
     } 

     PermutationCount++; 
    } 
} 

Answer 1

這是有點麻煩停止遞歸計算。最好的方法是使用全局變量（如果有對象，則使用私有類變量）。

這個變量表示，如果遞歸應停止與否：

bool stopRecursion = false; 

現在你計算你內心的每步之後更新這個變量：

if(_my_condition_is_met) stopRecursion = true; 

在你的遞歸調用方法開始你檢查這個變量的狀態：

public void CalcPermutation(int k) 
{ 
    if(stopRecursion) return; 
    ... 

而你檢查這個變量在尾部呃每次調用CalcPermutation：

for (int i = 0; i < ParametersClass.trainsToSchedule; i++) 
{ 
    //iterate until we come upon a slot in the array which has not been allocated an elements yet 
    if (permutationValue[i] == 0) 
    { 
     CalcPermutation(i); 
     if(stopRecursion) return; 
     .... 

有了這個方法，你儘快放鬆甚至深呼水平滿足您的停止條件。

Answer 2

for (int i = 0; i < ParametersClass.trainsToSchedule; i++) 
      { 
       //iterate until we come upon a slot in the array which has not been allocated an elements yet 
       if({your condition}){ 
        break; 
       } 
       if (permutationValue[i] == 0) 
       { 

        CalcPermutation(i); //rerun the code to allocate an element to the empty slot. the location of the empty slot is given as a parameter (this is how k increments) 

       } 
      } 

Answer 3

感謝大家的回覆。我設法讓它做的工作如下：

下CalcPermutation（我）線，我寫

if (permutationCount == ParametersClass.timetableNumber) 
{ 
     return; 
} 

我試着用不同的輸入運行了幾次，似乎工作得很好。