遞歸中的無限循環

Question

我正在整理一個代碼來輸出以下模式：

000000000X
00000000XX
0000000XXX
000000XXXX
00000XXXXX
0000XXXXXX
000XXXXXXX
00XXXXXXXX
0XXXXXXXXX

（每一行應該是一個接一個。我不太確定如何在論壇上顯示模式...對不起）

我應該在代碼內使用遞歸循環，但最終會陷入無限循環，我真的不明白為什么。（可以確定我實際上從沒有使用過遞歸循環）。是我的代碼：

class Recursion {
    //recursion should stop after 9 attempts
    static int stopindex = 9;

    public static void main(String[] args) {
        //a=number of "O"s and b=number of "X"s
        int a = 9;
        int b = 1;
        recursion(a, b);
    }
    public static void recursion(int a, int b) {

        //start of recursion at index 1
        int startindex = 1;

        //stop condition of recursion
        if (startindex == stopindex)
            return;

        //printing of pattern
        for (int i = a; i > 0; i--) {
            System.out.print("O");
        }
        for (int j = 0; j < b; j++) {
            System.out.print("X");
        }
        System.out.println();

        --a;
        ++b;
        ++startindex;
        recursion(a, b);
    }
}

Answer 1

你的算法略有偏差，你不應該有靜態變量，你不應該改變a，你的第一個for循環條件 - 我想你想要的，

public static void recursion(int a, int b) {
  // stop condition of recursion
  if (a == b) return;

  // printing of pattern
  for (int i = a - b; i > 0; i--) {
    System.out.print("O");
  }
  for (int j = 0; j < b; j++) {
    System.out.print("X");
  }
  System.out.println();

  // --a;
  ++b; // <-- this could be done in the recursion call below,
  recursion(a, b);
  // recursion(a, ++b); // <-- like that.
}

輸出是

OOOOOOOOX
OOOOOOOXX
OOOOOOXXX
OOOOOXXXX
OOOOXXXXX
OOOXXXXXX
OOXXXXXXX
OXXXXXXXX

Answer 2

您根本不需要startindex參數a就是您為遞歸制定暫停條件所需要的。 對於每次遞歸的recusion調用， a是一個少於一個，一旦a == 0你就打破了遞歸。

因此，您每次都將startindex重置為1因此斷開條件始終為false。

public static void recursion(int a, int b) {
    if (a == 0) {
       return;
    }

    // Print here

    recursion(a - 1, b + 1);
}

Answer 3

您要在遞歸方法的開始處重置變量startindex，因此，如果int startindex = 1 ;，則調用遞歸方法並將startindex增加一，然后再次調用該方法，變量將被重置。

class Recursion {
static int stopindex = 9;
int startindex = 1;
public static void main(String[] args) {
    //a=number of "O"s and b=number of "X"s
    int a = 9;
    int b = 1;
    recursion(a, b);
}
public static void recursion(int a, int b) {

    //start of recursion at index 1
    //int startindex = 1; - removed due to variable reset

    //stop condition of recursion
    if (startindex == stopindex)
        return;

    //printing of pattern
    for (int i = a; i > 0; i--) {
        System.out.print("O");
    }
    for (int j = 0; j < b; j++) {
        System.out.print("X");
    }
    System.out.println();

    --a;
    ++b;
    ++startindex;
    recursion(a, b);
}
}

Answer 4

您的問題是每次調用函數時都會重置啟動索引。 試試這個代碼

class Recursion {
//recursion should stop after 9 attempts
static int stopindex = 9;

public static void main(String[] args) {
    //a=number of "O"s and b=number of "X"s
    int a = 9;
    int b = 1;
    int startindex = 1;
    recursion(a, b, startindex);

}
public static void recursion(int a, int b, int startIndex) {

    //start of recursion at index 1


    //stop condition of recursion
    if (startIndex > stopindex)
        return;

    //printing of pattern
    for (int i = a; i > 0; i--) {
        System.out.print("O");
    }
    for (int j = 0; j < b; j++) {
        System.out.print("X");
    }
    System.out.println();

    --a;
    ++b;
    ++startIndex;
    recursion(a, b, startIndex);
}
}

產量

OOOOOOOOOX
OOOOOOOOXX
OOOOOOOXXX
OOOOOOXXXX
OOOOOXXXXX
OOOOXXXXXX
OOOXXXXXXX
OOXXXXXXXX
OXXXXXXXXX