在Java中需要遞歸方法的幫助

Question

我有點新來編程，需要幫助做一個遞歸方法。我有一個方法，在二維數組中選擇一個隨機空間，然後我想檢查空間是否空閒。如果空間是自由，我想使用的空間，但如果不是我想選擇一個新的隨機空間在2D array.Thanks

import java.io.* ; 
import java.util.ArrayList ; 
public class WordSearchPuzzle 
{ 
    private char[][] puzzle ; 
    private ArrayList<String> puzzleWords ; 
    private int letterCount = 0 ; 
    private int gridDimensions; 

    public WordSearchPuzzle(ArrayList<String> userSpecifiedWords) 
    { 
     this.puzzleWords = userSpecifiedWords ; 

    } 

    private void createPuzzleGrid() 
    { 
     int i, itemLength; 
     String item; 
     for (i = 0; i < puzzleWords.size(); i++) { 
      item = puzzleWords.get(i); 
      itemLength = item.length(); 
      letterCount = letterCount + itemLength; 
     } 
     gridDimensions = letterCount * 2; 
     puzzle = new char[gridDimensions][gridDimensions] ; 
    } 

    private void generateWordSearchPuzzle() 
    { 

    } 


    public void firstSpace(String Word) 
     { 
      int row, column; 
      row = (int)(Math.random() * gridDimensions +1); 
      column = (int)(Math.random() * gridDimensions +1); 
      if(puzzle[row][column] != ' '){ 
       firstSpace(); 
      } 
     } 

Answer 1

我不認爲在您的索引計算中加1是必要的，也可能會導致數組越界異常。儘管這取決於您對gridDimensions的定義。

您在註釋中指定的問題是因爲Java編譯器試圖找到名爲'void firstSpace（）'的方法，這是'void firstSpace（String word）'的一種不同方法。

public void firstSpace(String word) 
{ 
    int row, column; 

    // No need to add 1, Java arrays are accessed with the first index 
    // being 0. Math.random() returns from 0 up to but not including 1.0. 
    // e.g. array size = 50, min index = 0, max index = 49 
    // Lets say you get very close to 1 e.g. 0.9999, then 
    // 0.9999 * 50 = 49.995 (after integer truncating you have 49) 
    row = (int)(Math.random() * gridDimensions); 
    column = (int)(Math.random() * gridDimensions); 

    if(puzzle[row][column] != ' ') { 
     // If this element is not "empty" then run the method again 
     // using recursion. null might be a better choice to compare 
     // to depending on how you initialized the array. 
     firstSpace(word); 
    } else { 
     // Otherwise we're finished and we can set the array element 
     // to the new word. 

     // (Assumed post condition (you might want to do something else once you 
     // find a blank index)) 
     puzzle[row][column] = word; 
    } 
} 

Answer 2

您在評論中提到的具體問題，是因爲firstSpace方法需要有一個字符串作爲參數。您應該使用：

firstSpace(word); 

另外要注意，這種方法目前並不返回任何東西，所以你無法知道它選擇哪個空間的方式。