算法-归并排序

import java.util.Random;


public class MergeSort {
	
	
	//归并
	public static  void merge(int a[],int left,int mid,int right){
		int i=left;
		int j=mid+1;
		int k=0;
		int temp []=new int[right-left+1];
		//把两个数组归并
		while(i<=mid&&j<=right){
			if(a[i]<=a[j]){
				temp[k++]=a[i++];
			}else{
				temp[k++]=a[j++];
			}
		}
		
		//把左边的数组加入到temp里面
		while(i<=mid){
			temp[k++]=a[i++];
		}
		
		//把右边的数组加入到temp里面
		while(j<=right){
			temp[k++]=a[j++];
		}
		
		//把temp数组复制到a数组中
		for (int k2 = 0; k2 < temp.length; k2++){ 
			a[k2 + left] = temp[k2];
			}  

	}
	
	public static int[] mergeSort(int arr[], int left,int right){
		int mid=(left+right)/2;
		if(left<right){
			mergeSort(arr,left,mid);
			mergeSort(arr, mid+1, right);
			merge(arr,left,mid,right);
		}
	
		return arr;
	}
	
	public static  void main(String args[]){
		int a[]=new int[20];
		Random random=new Random();
		for(int i=0;i<a.length;i++){
			a[i]=random.nextInt(100);
		}
		int arr[]=mergeSort(a,0,a.length-1);
		for(int i=0 ;i<arr.length;i++){
			System.out.print(arr[i]+"\t");
		}
		System.out.println();
		
		
	}
}