我试图在Java中反转一个int数组。

此方法不反转数组。

for(int i = 0; i < validData.length; i++)
{
    int temp = validData[i];
    validData[i] = validData[validData.length - i - 1];
    validData[validData.length - i - 1] = temp;
}

有什么问题吗?


当前回答

下面是要在您的机器上运行的完整程序。

public class ReverseArray {
    public static void main(String[] args) {
        int arr[] = new int[] { 10,20,30,50,70 };
        System.out.println("reversing an array:");
        for(int i = 0; i < arr.length / 2; i++){
            int temp = arr[i];
            arr[i] = arr[arr.length - i - 1];
            arr[arr.length - i - 1] = temp;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }   
    }
}

对于矩阵上使用数组的程序,这将是很好的来源。通过链接。

其他回答

这里是一个简单的实现,反转数组的任何类型,加上全/部分支持。

import java.util.logging.Logger;

public final class ArrayReverser {
 private static final Logger LOGGER = Logger.getLogger(ArrayReverser.class.getName());

 private ArrayReverser () {

 }

 public static <T> void reverse(T[] seed) {
    reverse(seed, 0, seed.length);
 }

 public static <T> void reverse(T[] seed, int startIndexInclusive, int endIndexExclusive) {
    if (seed == null || seed.length == 0) {
        LOGGER.warning("Nothing to rotate");
    }
    int start = startIndexInclusive < 0 ? 0 : startIndexInclusive;
    int end = Math.min(seed.length, endIndexExclusive) - 1;
    while (start < end) {
        swap(seed, start, end);
        start++;
        end--;
    }
}

 private static <T> void swap(T[] seed, int start, int end) {
    T temp =  seed[start];
    seed[start] = seed[end];
    seed[end] = temp;
 }  

}

下面是相应的单元测试

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;

import org.junit.Before;
import org.junit.Test;

public class ArrayReverserTest {
private Integer[] seed;

@Before
public void doBeforeEachTestCase() {
    this.seed = new Integer[]{1,2,3,4,5,6,7,8};
}

@Test
public void wholeArrayReverse() {
    ArrayReverser.<Integer>reverse(seed);
    assertThat(seed[0], is(8));
}

 @Test
 public void partialArrayReverse() {
    ArrayReverser.<Integer>reverse(seed, 1, 5);
    assertThat(seed[1], is(5));
 }
}
public class ArrayHandle {
    public static Object[] reverse(Object[] arr) {
        List<Object> list = Arrays.asList(arr);
        Collections.reverse(list);
        return list.toArray();
    }
}

上面有一些很棒的答案,但我是这样做的:

public static int[] test(int[] arr) {

    int[] output = arr.clone();
    for (int i = arr.length - 1; i > -1; i--) {
        output[i] = arr[arr.length - i - 1];
    }
    return output;
}

最有效的方法是向后迭代数组。

我不确定Aaron的解决方案是否调用Collections.reverse(list);有人知道吗?

以下是我想到的:

// solution 1 - boiler plated 
Integer[] original = {100, 200, 300, 400};
Integer[] reverse = new Integer[original.length];

int lastIdx = original.length -1;
int startIdx = 0;

for (int endIdx = lastIdx; endIdx >= 0; endIdx--, startIdx++)
   reverse[startIdx] = original[endIdx];

System.out.printf("reverse form: %s", Arrays.toString(reverse));

// solution 2 - abstracted 
// convert to list then use Collections static reverse()
List<Integer> l = Arrays.asList(original);
Collections.reverse(l);
System.out.printf("reverse form: %s", l);