【Java】 归并排序的非递归实现

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++];
			else
				temp[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();
	}
}