英文:
Is there any built-un function in Java to reverse the array from one specified index to another index?
问题
例如：
我的数组是[1,2,3,4]，我想要将索引从1到2的部分反转。因此，我的答案应为[1,3,2,4]。
我该如何实现这个？
英文:
For example:
My array is [1,2,3,4] and I want to reverse it from index 1 to 2. So my answer should be [1,3,2,4].
How can I achieve this?
答案1
得分: 1
这很简单：
public static void reverseRangeClose(int[] arr, int fromIndexInclusive, int toIndexInclusive) {
for (int i = fromIndexInclusive, j = toIndexInclusive; i < j; i++, j--) {
int tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
}
输出：
int[] arr = { 1, 2, 3, 4 };
System.out.println(Arrays.toString(arr)); // [1, 2, 3, 4]
reverseRangeClose(arr, 0, 2);
System.out.println(Arrays.toString(arr)); // [3, 2, 1, 4]
英文:
This is very simple:
public static void reverseRangeClose(int[] arr, int fromIndexInclusive, int toIndexInclusive) {
for (int i = fromIndexInclusive, j = toIndexInclusive; i < j; i++, j--) {
int tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
}
Output:
int[] arr = { 1, 2, 3, 4 };
System.out.println(Arrays.toString(arr)); // [1, 2, 3, 4]
reverseRangeClose(arr, 0, 2);
System.out.println(Arrays.toString(arr)); // [3, 2, 1, 4]
答案2
得分: 0
如果您将数组指定为对象数组而不是基本数组，则可以按以下方式进行操作。
Integer[] a = {1,2,3,4,5,6,7,8,9,10};
Collections.reverse(Arrays.asList(a).subList(3,7));
System.out.println(Arrays.toString(a));
它能够工作是因为Arrays.asList使用您的数组作为列表的支持。子列表指定要反转的列表（从而也反转了数组）的部分。
打印结果
[1, 2, 3, 7, 6, 5, 4, 8, 9, 10]
对于基本数组，您可以按以下方式操作。这就是@Andreas所谈论的内容。唯一的区别在于结束索引是“排除”的，以符合大多数语言中指定范围的标准做法。并且当起始索引大于结束索引时，我还会抛出异常。
public static void reverse(int[] a, int begin, int end) {
if (begin > end) {
throw new IllegalArgumentException(
String.format("begin(%d) > end(%d)", begin, end));
}
for (int i = begin, j = end-1; i < j; i++, j--) {
int t1 = a[i];
a[i] = a[j];
a[j] = t1;
}
}
英文:
If you specify your array as an Object array and not a primitive array you can do it like this.
Integer[] a = {1,2,3,4,5,6,7,8,9,10};
Collections.reverse(Arrays.asList(a).subList(3,7));
System.out.println(Arrays.toString(a));
It works because the Arrays.asList uses your array to back up the list. The sublist specifies which part of the list (and thus the array) to reverse.
Prints
[1, 2, 3, 7, 6, 5, 4, 8, 9, 10]
For a primitive array, you can do it like this. This is what @Andreas was talking about. The only difference is that the end is exclusive to conform to standard practices in most languages when specifying ranges. And I also throw an exception when the beginning index is greater than the ending index.
public static void reverse(int[] a, int begin, int end) {
if (begin > end) {
throw new IllegalArgumentException(
String.format("begin(%d) > end(%d)", begin, end));
}
for (int i = begin, j = end-1; i < j; i++, j--) {
int t1 = a[i];
a[i] = a[j];
a[j] = t1;
}
}
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