归并排序（Merge-Sort）

归并排序是一种比插入排序更加高效的排序算法，尤其是规模较大的时候，其时间复杂度为O(nlgn)而插入排序为O(n²)，下面给出数组的归并排序的Java实现代码

/** * Created by CvShrimp on 2017/9/26. */public class MergeSort {    public static void mergeSort(int[] array, int startIndex, int endIndex) {        if(startIndex >= endIndex) return;        int midIndex = (startIndex + endIndex) / 2;        //使用分治法，每次把待排序的数组分成两部分        mergeSort(array, startIndex, midIndex);        mergeSort(array, midIndex + 1, endIndex);        merge(array, startIndex, midIndex , endIndex);    }    public static void merge(int[] array, int startIndex, int midIndex, int endIndex) {        int i = startIndex;        int j = midIndex + 1;        int[] tempArray = new int[endIndex - startIndex + 1];        int tempIndex = 0;        while (i <= midIndex && j <= endIndex) {            if(array[i] <= array[j]) {                tempArray[tempIndex] = array[i];                i++;                tempIndex++;            }else {                tempArray[tempIndex] = array[j];                j++;                tempIndex++;            }        }        while (i <= midIndex) {            tempArray[tempIndex] = array[i];            i++;            tempIndex++;        }        while (j <= endIndex) {            tempArray[tempIndex] = array[j];            j++;            tempIndex++;        }        for(int k = 0; k < tempArray.length; k++) {            array[startIndex + k] = tempArray[k];        }    }    public static void main(String[] args) {        int[] array = {1,5,7,8,9,2,0,6,16,12};        mergeSort(array, 0, array.length - 1);        System.out.print("Sorted result: ");        for(int single : array) {            System.out.print(single + " ");        }        System.out.println();    }}