归并排序（Java）
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归并排序介绍
归并排序（MERGE-SORT）是利用归并的思想实现的排序方法，该算法采用经典的分治（divide-and-conquer）策略（分治法将问题分(divide)成一些小的问题然后递归求解，而治(conquer)的阶段则将分的阶段得到的各答案"修补"在一起，即分而治之)。
代码
package cn.guizimo.sort;
import java.util.Arrays;
public class MergetSort {
public static void main(String[] args) {
int arr[] = {8, 4, 5, 7, 1, 3, 6, 2};
int temp[] = new int[arr.length];
System.out.println("排序前");
System.out.println(Arrays.toString(arr));
mergeSort(arr, 0, arr.length - 1, temp);
System.out.println("排序后");
System.out.println(Arrays.toString(arr));
}
public static void mergeSort(int[] arr, int left, int right, int[] temp) {
if (left < right) {
int mid = (left + right) / 2;
mergeSort(arr, left, mid, temp);
mergeSort(arr, mid + 1, right, temp);
merge(arr, left, mid, right, temp);
}
}
public static void merge(int[] arr, int left, int mid, int right, int[] temp) {
int i = left;
int j = mid + 1;
int t = 0;
while (i <= mid && j <= right) {
if (arr[i] <= arr[j]) {
temp[t] = arr[i];
t += 1;
i += 1;
} else {
temp[t] = arr[j];
t += 1;
j += 1;
}
}
while (i <= mid) {
temp[t] = arr[i];
t += 1;
i += 1;
}
while (j <= right) {
temp[t] = arr[j];
t += 1;
j += 1;
}
t = 0;
int tempIndex = left;
while (tempIndex <= right) {
arr[tempIndex] = temp[t];
t += 1;
tempIndex += 1;
}
}
}
测试
速度测试
package cn.guizimo.sort;
import java.util.Arrays;
public class MergetSort {
public static void main(String[] args) {
int max = 80000;
int[] arr = new int[max];
for (int i = 0; i < max; i++) {
arr[i] = (int)(Math.random() * 8000000);
}
int temp[] = new int[arr.length];
long date1 = System.currentTimeMillis();
mergeSort(arr, 0, arr.length - 1, temp);
long date2 = System.currentTimeMillis();
System.out.println("归并排序"+max+"数组的时间为："+(date2-date1));
}
public static void mergeSort(int[] arr, int left, int right, int[] temp) {
if (left < right) {
int mid = (left + right) / 2;
mergeSort(arr, left, mid, temp);
mergeSort(arr, mid + 1, right, temp);
merge(arr, left, mid, right, temp);
}
}
public static void merge(int[] arr, int left, int mid, int right, int[] temp) {
int i = left;
int j = mid + 1;
int t = 0;
while (i <= mid && j <= right) {
if (arr[i] <= arr[j]) {
temp[t] = arr[i];
t += 1;
i += 1;
} else {
temp[t] = arr[j];
t += 1;
j += 1;
}
}
while (i <= mid) {
temp[t] = arr[i];
t += 1;
i += 1;
}
while (j <= right) {
temp[t] = arr[j];
t += 1;
j += 1;
}
t = 0;
int tempIndex = left;
while (tempIndex <= right) {
arr[tempIndex] = temp[t];
t += 1;
tempIndex += 1;
}
}
}
感谢
尚硅谷
万能的网络
以及勤劳的自己
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