用java 写个归并排序
时间: 2023-07-17 22:04:31 浏览: 40
下面是使用Java编写的归并排序示例代码:
```java
public class MergeSort {
public static void merge(int[] arr, int left, int mid, int right) {
int n1 = mid - left + 1;
int n2 = right - mid;
int[] leftArr = new int[n1];
int[] rightArr = new int[n2];
for (int i = 0; i < n1; ++i)
leftArr[i] = arr[left + i];
for (int j = 0; j < n2; ++j)
rightArr[j] = arr[mid + 1 + j];
int i = 0, j = 0;
int k = left;
while (i < n1 && j < n2) {
if (leftArr[i] <= rightArr[j]) {
arr[k] = leftArr[i];
i++;
} else {
arr[k] = rightArr[j];
j++;
}
k++;
}
while (i < n1) {
arr[k] = leftArr[i];
i++;
k++;
}
while (j < n2) {
arr[k] = rightArr[j];
j++;
k++;
}
}
public static void mergeSort(int[] arr, int left, int right) {
if (left < right) {
int mid = (left + right) / 2;
mergeSort(arr, left, mid);
mergeSort(arr, mid + 1, right);
merge(arr, left, mid, right);
}
}
public static void main(String[] args) {
int[] arr = { 12, 11, 13, 5, 6, 7 };
int n = arr.length;
System.out.println("原始数组:");
for (int num : arr) {
System.out.print(num + " ");
}
System.out.println();
mergeSort(arr, 0, n - 1);
System.out.println("排序后的数组:");
for (int num : arr) {
System.out.print(num + " ");
}
}
}
```
这段代码实现了归并排序算法。通过 `mergeSort` 方法对数组进行递归地拆分和合并,而 `merge` 方法用于合并两个有序子数组。在 `main` 方法中,我们可以看到如何使用归并排序对一个整数数组进行排序。