归并排序

归并排序是先将待排序的数据分为左右两部分，分别对左右两部分递归，再将排序后的左右两部分归并排序

O(nlogn)

import java.util.Arrays;
class Main{
    static int[] nums = {2,7,8,3,1,6,9,0,5,4};
    
    public static void mergeSort(int low,int high){
        if(low<high){
            int mid = (low+high)/2;
            mergeSort(low,mid);
            mergeSort(mid+1,high);
            merge(low,mid,high);
        }
    }
    
    public static void merge(int low,int mid,int high){
        int[] temp = new int[high-low+1];
        int i = low;
        int j = mid +1;
        int k = 0;
        
        while(i<=mid&&j<=high){
            if(nums[i]<nums[j])
                temp[k++] = nums[i++];
            else
                temp[k++] = nums[j++];
        }
        while(i<=mid){
            temp[k++] = nums[i++];
        }
        while(j<=high){
            temp[k++] = nums[j++];
        }
        
        for(int p=0;p<temp.length;p++){
            nums[p+low] = temp[p];
        }
    }
    
    public static void main(String[] args){
        mergeSort(0,nums.length-1);
        System.out.println(Arrays.toString(nums));
    }
}