二维数组转字符串代码java
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2 dimensional array to string code java
提问by Alex A
For a program I have to write I am required to turn a 2 dimensional array of single digit intgers into a string of numbers separated by spaces. A test code is provided for me and when I run it, my code fails both arrayToString tests. I am unable to find where my logic error is. Someone help!
对于我必须编写的程序，我需要将单个数字整数的二维数组转换为由空格分隔的数字字符串。为我提供了一个测试代码，当我运行它时，我的代码在两个 arrayToString 测试中都失败了。我找不到我的逻辑错误在哪里。有人帮忙！
public static String arrayToString(int[][] a) {
String aString;
aString = "";
int column;
int row;
for (row = 0; row < a.length; row++) {
for (column = 0; column < a[0].length; column++ ) {
aString = aString + " " + a[row][column];
}
aString = aString + "\n";
}
return aString;
}
回答by Bohemian
Your code is basically OK, except you are putting a leading space at the start of every line. To clean them up before returning, add this line:
您的代码基本上没问题，只是您在每一行的开头放置了一个前导空格。要在返回之前清理它们，请添加以下行：
aString = aString.replaceAll("(?m)^ ", "");
This uses regex to delete (by replacing with a blank) all spaces at the start of lines. The regex flag (?m)makes ^match the start of every line of the input (normally ^matches only the start of input).
这使用正则表达式删除（通过用空格替换）行首的所有空格。正则表达式标志(?m)品牌^匹配输入的每一行（通常的开始^只输入开始相匹配）。
回答by Dawood ibn Kareem
I can think of three possible issues.
我能想到三个可能的问题。
- The test code doesn't want to see the space that you are putting at the beginning of every line.
- The test code is passing an array where some of the entries are null. Your code doesn't cope with this.
- The test code is passing an array where the entries have different lengths. Your code doesn't cope with this either.
- 测试代码不想看到您在每一行开头放置的空间。
- 测试代码正在传递一个数组，其中一些条目为空。您的代码无法解决此问题。
- 测试代码正在传递一个数组，其中条目具有不同的长度。您的代码也无法解决此问题。
Until you post the test code, we can't see which one the problem is. But you could deal with all three by changing your loop to this.
在您发布测试代码之前，我们无法看到问题出在哪一个。但是您可以通过将循环更改为此来处理所有三个。
for (row = 0; row < a.length; row++) {
if (a[row] != null && a[row].length > 0) {
aString = aString + a[row][0];
for (column = 1; column < a[row].length; column++) {
aString = aString + " " + a[row][column];
}
}
aString = aString + "\n";
}
回答by Martin
int[][] a = new int[][]{{1,2,3},{4,5,6},{7,8,9}};
public static String arrayToString(int[][] a) {
String aString;
aString = "";
int column;
int row;
for (row = 0; row < a.length; row++) {
for (column = 0; column < a[0].length; column++ ) {
aString = aString + " " + a[row][column];
}
aString = aString + "\n";
}
return aString;
}
Output:
输出：
1 2 3
4 5 6
7 8 9
If you skip this line aString = aString + "\n";your output will look like this
如果您跳过这一行，aString = aString + "\n";您的输出将如下所示
1 2 3 4 5 6 7 8 9
回答by Valentin Michalak
@dawood-ibn-kareem explain good the possible cause of the failure of the test.
@dawood-ibn-kareem 很好地解释了测试失败的可能原因。
With Java 8 Stream, it's pretty easy to do what you want!
使用 Java 8 Stream，可以很容易地做你想做的事！
With the input: [[1,2,3], [3,4,5], [5,6,7]]
随着输入：[[1,2,3], [3,4,5], [5,6,7]]
public static String arrayToString(int[][] a) {
return Arrays.stream(a)
.map(s -> Arrays.stream(s)
.mapToObj(String::valueOf)
.collect(Collectors.joining(" "))
)
.collect(Collectors.joining("\n"));
}
Output:
输出：
1 2 3
3 4 5
5 6 7
Other method, to separate each line of the 2D array without carriage return
其他方法，将二维数组的每一行分开，不用回车
public static String arrayToString(int[][] a) {
return Arrays.stream(a)
.flatMapToInt(Arrays::stream)
.mapToObj(String::valueOf)
.collect(Collectors.joining(" "));
}
Output
输出
1 2 3 3 4 5 5 6 7
Have fun!
玩得开心！
