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10810-Ultra-QuickSort.cpp
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10810-Ultra-QuickSort.cpp
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#include<bits/stdc++.h>
using namespace std;
vector<long long>a;
long long ans=0;
void inversion(int l, int mid, int r)
{
int n1=mid-l+1;
int n2=r-mid;
vector<int>tempL(n1+1), tempR(n2+1);
for(int i=0; i<n1; i++)
tempL[i]=a[l+i];
for(int i=0; i<n2; i++)
tempR[i]=a[mid+i+1];
int i=0, j=0;
int k=l;
while(i<n1 && j<n2)
{
if(tempL[i]>tempR[j])
{
a[k++]=tempR[j++];
ans+=(n1-i);
}
else
a[k++]=tempL[i++];
}
while(i<n1)
a[k++]=tempL[i++];
while(j<n2)
a[k++]=tempR[j++];
}
void mergesort(int l, int r)
{
if(l<r)
{
int mid=(l+r)/2;
mergesort(l, mid);
mergesort(mid+1, r);
inversion(l, mid, r);
}
}
int main()
{
freopen("/home/ornob/Downloads/Practice/input.txt", "r", stdin);
freopen("/home/ornob/Downloads/Practice/output.txt", "w", stdout);
int n;
while(cin>>n)
{
if(n==0)
break;
int x;
for(int i=0; i<n; i++)
{
cin>>x;
a.push_back(x);
}
mergesort(0, n-1);
cout<<ans<<endl;
ans=0;
a.clear();
}
return 0;
}