归并排序(Java)
< 返回列表时间: 2020-06-27来源:OSCHINA
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; } } }

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