public class MergeSort2 {public void mergeSort(int[] arr) {if(arr==null || arr.length<=0)return;int width = 1;while(width<arr.length) {mergePass(arr,width);width*=2; }}private void mergePass(int[] arr,int width) {int start=0;while(start+2*width-1<arr.length) {int mid=start+width-1;int end=start+2*width-1;merge(arr,start,mid,end);start=start+2*width;}//剩余无法构成完整的两组也要进行处理if(start+width-1<arr.length) merge(arr, start, start+width-1, arr.length-1);}private void merge(int[] arr, int start, int mid, int end) {int i=start;int j=mid+1;int[] temp = new int[end-start+1];int index=0;while(i<=mid && j<=end) {if(arr[i]<=arr[j])temp[index++]=arr[i++];elsetemp[index++]=arr[j++];}while(i<=mid)temp[index++]=arr[i++];while(j<=end)temp[index++]=arr[j++];for(int k=start;k<=end;k++)arr[k]=temp[k-start];}//==========测试代码=================public void test1() {int[] a = null;mergeSort(a);System.out.println(Arrays.toString(a));}public void test2() {int[] a = {};mergeSort(a);System.out.println(Arrays.toString(a));}public void test3() {int[] a = { 1 };mergeSort(a);System.out.println(Arrays.toString(a));}public void test4() {int[] a = { 3, 3, 3, 3, 3 };mergeSort(a);System.out.println(Arrays.toString(a));}public void test5() {int[] a = { -3, 6, 3, 1, 3, 7, 5, 6, 2 };mergeSort(a);System.out.println(Arrays.toString(a));}public static void main(String[] args) {MergeSort2 demo =new MergeSort2();demo.test1();demo.test2();demo.test3();demo.test4();demo.test5();}
}