【算法学习】归并排序

public class mergesort{
    public static void mergeSort(int[] arr, int l, int r) {
        if(l<r){
            int mid=l+(r-l)/2;
            mergeSort(arr,l,mid);
            mergeSort(arr,mid+1,r);
            merge(arr,l,r);
        }
    }
    
    public void merge(int[] arr,int l,int r){
        int[] tmp=new int[r-l+1];
        int mid=l+(r-l)/2;int p1=l;
        int p2=mid+1;
        int i=0;
        while(p1<=m&&p2<=r){
            if(arr[p1]<arr[p2])
                tmp[i++]=arr[p1++];
            else
                tmp[i++]=arr[p2++];
        }
        while(p1<=m)
            tmp[i++]=arr[p1];
        while(p2<=r)
            tmp[i++]=arr[p2];
        for(i=0;i<arr.length;i++){
            arr[l+i]=tmp[i];
        }
    }
}