java需要修复for循环

Question

我在上在线课程，这让我很难得到帮助，这就是我来这里的原因。本周的讲座是关于嵌套循环的。他们把我弄糊涂了。我目前被困在这个问题上

Given numRows and numColumns, print a list of all seats in a theater. Rows are numbered, columns lettered, as in 1A or 3E. Print a space after each seat, including after the last. Use separate print statements to print the row and column. Ex: numRows = 2 and numColumns = 3 prints:

1A 1B 1C 2A 2B 2C &燃气轮机

我尝试了许多可能的解决办法，但都产生了许多错误的结果。这是我目前的解决方案

    int numRows;
      int numColumns;
      int currentRow;
      int currentColumn;
      char currentColumnLetter;

      numRows = scnr.nextInt();
      numColumns = scnr.nextInt();

      currentColumnLetter = 'A'; 

         for (currentRow = 1; currentRow <= numRows; currentRow++)
         {

             for (currentColumn = 1; currentColumn < numColumns; currentColumn++)

             {
               System.out.print(currentRow);
               System.out.print(currentColumnLetter + " "); 

             }

              if( currentColumn == numColumns)
               {
                  currentColumnLetter++;
               }
         }

代码产生了这个结果

1A 1A 2B 2B 

期望的结果是

1A 1B 2A 2B

我已经做了两天了，这让我非常沮丧。提前感谢您的帮助

Answer 1

你很接近

但是，您没有正确处理列名。当每一行开始时，您需要返回到A，并对每一列按一递增：

for (currentRow = 1; currentRow <= numRows; currentRow++) {
    currentColumnLetter = 'A'; //Starting a new row, reset the column to `A`
    for (currentColumn = 1; currentColumn < numColumns; currentColumn++){
        System.out.print(currentRow); 
        System.out.print(currentColumnLetter + " ");
        currentColumnLetter++;
    }
}

使用基于1的索引也很奇怪。Java（以及许多其他语言）中的索引应该从0开始。因此，列循环没有执行足够的迭代-如果将numColumns设置为2，则只打印单个列

这样写循环会更习惯：

for (currentRow = 0; currentRow < numRows; currentRow++) {
    currentColumnLetter = 'A';
    for (currentColumn = 0; currentColumn < numColumns; currentColumn++) {
        System.out.print(currentRow + 1);
        System.out.print(currentColumnLetter + " ");
        currentColumnLetter++;
    }
}

Answer 2

哟，事情比你想象的还要深刻。我总是觉得这些重复的人物例子很糟糕，我在上次的工作面试中就知道了。现在我们开始：

如果练习是这样的：从1获取行。。n、 1.的列。。n、 输出应为“1/1，1/2…3/1，3/2…”，这是直截了当的，不是吗

public void seatnumbersNumbersOnly() {
        int numRows = 3;
        int numColumns = 3;

        for (int currentRow = 1; currentRow <= numRows; currentRow++) {
            for (int currentColumn = 1; currentColumn < numColumns; currentColumn++) {
                System.out.print(currentColumn + "/" + currentRow + " ");
            }
        }
    }

但任务是不同的，他们希望列中有字母。让我们在同样的基础上对其进行暴力

public void seatnumbersNumbersMappedAgain() {
String[] seatLetters = new String []{"A", "B", "C"}; // so many letters as there are columns. Note: array index is 0-based
int numRows = 3;
int numColumns = 3;

for (int currentRow = 1; currentRow <= numRows; currentRow++) {
    for (int currentColumn = 1; currentColumn < numColumns; currentColumn++) {
        // seatLetters[i] is a string "s", not a char 'c', so everything's fine
        System.out.print(seatLetters[currentColumn - 1] + currentRow + " "); // -1: seatLetters indexing is zero based
    }
}

}

但是：在Java中，字符和字节是可互换的，只要您在ascii范围内，就可以将字符文本分配给字节，反之亦然

@Test
public void charByteEquivalence() {
    // check out http://www.asciitable.com/
    char ca = 'A';
    byte ba = 0x41;
    assertEquals(ca, ba);

    ca = 0x41;
    ba = 'A';
    assertEquals(ca, ba);
}

这意味着，您还可以直接使用char变量进行循环。但是请注意，构建输出字符串会变得很混乱，因为您必须观察哪些内容会被“+”加上哪些内容。您需要列的字符串/字符值和行的数字。A "string" + char/byte/int。。。变成一个字符串char + int变成和int？一个字节？炭？当然不是一根绳子。披露：我尝试了字符串连接并出错，它变成了一个int。隐式类型转换的一些示例是here，官方引用是here

    public void seatnumbersChar() {
    int numRows = 3;
    int numColumns = 3;

    char firstColumnLetter = 'A';
    for (int currentRow = 1; currentRow <= numRows; currentRow++) {
        for (char currentColumn = firstColumnLetter; currentColumn < firstColumnLetter + numColumns; currentColumn++) {
            // at this point you have to watch out currentColumn + currentRow + " " will get evaluated left to right

            // currentRow is an int
            // currentColumn becomes an int when "+"ed with currentRow 
            // so currentRow + currentColumn would add two numbers instead of concatenating 2 strings, therefore
            // an explicit conversion to string is needed for one of the arguments
            System.out.print(currentColumn + String.valueOf(currentRow) + " ");
        }
    }
}

同样的例子是字节路由，类似的字符串连接混乱，但不完全相同

public void seatnumbersByte() {
    int numRows = 3;
    int numColumns = 3;

    byte firstColumnLetter = 'A';
    for (int currentRow = 1; currentRow <= numRows; currentRow++) {
        for (byte currentColumn = firstColumnLetter; currentColumn < firstColumnLetter + numColumns; currentColumn++) {
            // same case other trick: (currentRow + " ") forces the result to be a string due to the + " "
            // currentColumn here is declared as byte, when concatenated to a string the numeric representation would be taken (wtf...?)
            // therefore a cast to char is needed "(char) currentColumn"
            // what's left now ? (currentRow + " ") is a string
            // "(char) currentColumn" is a char
            // a char "+" a string is a string
            System.out.print((char) currentColumn + (currentRow + " "));
        }
    }
}

希望我能在上次面试中报仇。不管怎样，我还是得到了这份工作；）

Answer 3

您需要在内部循环中增加currentColumnLetter。记住，对于每一行，您需要遍历每一列。这就是为什么要嵌套循环，对吗

试试这个：

for (currentRow = 1; currentRow <= numRows; currentRow++) {
    currentColumnLetter = 'A';
    for (currentColumn = 1; currentColumn <= numColumns; currentColumn++) {
        System.out.print(currentRow);
        System.out.print(currentColumnLetter + " "); 
        currentColumnLetter++ 
    }
}

在外循环中不需要此条件：

if( currentColumn == numColumns)
{
    currentColumnLetter++;
}