数组中的逆序对

class Solution {
public:
int InversePairs(vector<int> data) {
if(data.empty())
return 0;
int n=data.size();
vector<int> copy(n);
return Inverse(data,copy,0,n-1);
}
int Inverse(vector<int> &data,vector<int> ©,int start,int end)
{
if(start==end)
{
return 0;
}
int mid=(start+end)>>1;
int left=Inverse(data,copy,start,mid);
int right=Inverse(data,copy,mid+1,end);
int count=0;
int ll=mid;
int rr=end;
int k=end;
while(ll>=start&&rr>mid)
{
if(data[ll]>data[rr])
{
count+=rr-mid;
copy[k--]=data[ll--];
}
else
{
copy[k--]=data[rr--];
}
}
while(ll>=start)
copy[k--]=data[ll--];
while(rr>mid)
copy[k--]=data[rr--];
for(int i=start;i<=end;i++)
data[i]=copy[i];
return left+right+count;
}
};