hdu 4911 归并排序求逆序数

#include<stdio.h>
#define N 100005
int a
,tmp
;
long long s;
void merge(int l,int mid,int r)
{
    int i,j,k;
    i=l;j=mid+1;k=1;
    while(i<=mid&&j<=r)
    {
        if(a[i]>a[j])
        {
            tmp[k++]=a[j++];
            s+=mid-i+1;
        }
        else
        {
            tmp[k++]=a[i++];
        }
    }
    while(i<=mid)
        tmp[k++]=a[i++];
    while(j<=r)
        tmp[k++]=a[j++];
    k=1;
    for(i=l;i<=r;i++)
    {
        a[i]=tmp[k++];
    }
}
void mergesort(int l,int r)
{
        if(l==r)return ;
        int mid=(l+r)>>1;
        mergesort(l,mid);
        mergesort(mid+1,r);
        merge(l,mid,r);

}
int main()
{
    int n,k,i;
    while(scanf("%d%d",&n,&k)!=EOF)
    {
        s=0;
        for(i=1;i<=n;i++)
            scanf("%d",&a[i]);
        mergesort(1,n);
        if(s>k)
            s-=k;
        else
            s=0;
        printf("%I64d\n",s);
    }
    return 0;
}