java算法----排序----（5）归并排序

 package log;

 import java.util.Arrays;

 public class Test4 {

     /**
      * java算法---归并排序
      *
      * @param args
      */
     public static void main(String[] args) {
         // 需要排序的数组
         int arr[] = { 49, 20, 36, 51, 18, 94, 61, 31, 50 };
         // 循环输出该数组内容
         System.out.println("排序之前：");
         for (int a : arr) {
             System.out.print(a + "\t");
         }
         System.out.println();

         sort(arr, 0, arr.length - 1);
         // 循环输出该数组内容
         System.out.println("排序之后：");
         for (int a : arr) {
             System.out.print(a + "\t");
         }
         System.out.println();

     }

     public static void merge(int[] list, int left, int center, int right) {
         int[] tempArr = new int[list.length];
         int mid = center + 1;
         int third = left;
         int temp = left;
         while (left <= center && mid <= right) {
             if (list[left] <= list[mid]) {
                 tempArr[third++] = list[left++];
             } else {
                 tempArr[third++] = list[mid++];
             }
         }
         while (mid <= right) {
             tempArr[third++] = list[mid++];
         }
         while (left <= center) {
             tempArr[third++] = list[left++];
         }
         while (temp <= right) {
             list[temp] = tempArr[temp++];
         }
         System.out.println(Arrays.toString(list));
     }

     public static void sort(int[] list, int left, int right) {
         if (left < right) {
             int center = (left + right) / 2;
             sort(list, left, center);
             sort(list, center + 1, right);
             merge(list, left, center, right);
         }
     }

 }

下面是控制台的输出结果

归并排序是将两个或者两个以上有序表合并成一个新的有序表，即把带排序序列分为若干个子序列，每个子序列都是有序的。然后再把有序子序列合并为整体有序序列。