归并排序

import java.lang.reflect.Array;

import java.util.Arrays;

import java.util.Collections;

import java.util.List;



public class Test {

	public static int[] sort(int[] nums, int low, int high) {

		//System.out.println(Arrays.toString(nums));

		

		int mid = (low + high) / 2;

		System.out.println(low + " " + mid + " " +  high);

		if (low < high) {

			// 左边

			sort(nums, low, mid);

			// 右边

			sort(nums, mid + 1, high);

			// 左右归并

			

			System.out.println("beg merge --- " + low + " " + mid + " " +  high);

			merge(nums, low, mid, high);

			System.out.println(Arrays.toString(nums));

		}

		 

		return nums;

	}



	public static void merge(int[] nums, int low, int mid, int high) {

		int[] temp = new int[high - low + 1];

		int i = low;     // 左指针

		int j = mid + 1; // 右指针

		int k = 0;       // 临时数组指针



		// 把较小的数先移到新数组中

		// mid作为分界点比较

		while (i <= mid && j <= high) {

			if (nums[i] < nums[j]) {

				temp[k++] = nums[i++];

			} else {

				temp[k++] = nums[j++];

			}

		}

		

		System.out.println("1" + Arrays.toString(temp));



		// 把左边剩余的数移入数组

		while (i <= mid) {

			temp[k++] = nums[i++];

		}

		

		System.out.println("2 " + Arrays.toString(temp));



		// 把右边边剩余的数移入数组

		while (j <= high) {

			temp[k++] = nums[j++];

		}

		System.out.println("3 " + Arrays.toString(temp));



		// 把新数组中的数覆盖nums数组

		for (int k2 = 0; k2 < temp.length; k2++) {

			nums[k2 + low] = temp[k2];

		}

	}



	public static void main(String[] args) {

		// TODO Auto-generated method stub

		int[] nums = {5, 4, 3, 2, 1};// 6, 9, 0, 5, 4 };

		System.out.println(Arrays.toString(nums));



		sort(nums, 0, nums.length - 1);

		System.out.println(Arrays.toString(nums));



		Integer[] a = new Integer[] { 3, 2, 32, 3 };

		List<Integer> list = (List<Integer>) Arrays.asList(a);



		Collections.sort(list);



		for (int i = 0; i < list.size(); i++) {

			System.out.println(list.get(i));

		}



		System.out.println("test");

	}



}

 

Collections.sort(list); 里使用的归并排序
其实就是对数组递归拆分两个数组，或者更多，然后几个数组进行归并，然后依次添加到临时数组中， 临时数组最后也是有序的，然后再用临时数组来修改原数组.