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43 lines (39 loc) · 972 Bytes
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Copy pathEURON.cpp
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43 lines (39 loc) · 972 Bytes
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#include <iostream>
#include <vector>
using namespace std;
long long int ans = 0;
void merge(vector<int> &L, vector<int> &R, vector<int> &S){
int i=0, j=0;
while(i<L.size() and j<R.size()){
if(L[i]<=R[j]) S.push_back(L[i++]);
else{
ans += L.size()-i;
S.push_back(R[j++]);
}
}
while(i<L.size()) S.push_back(L[i++]);
while(j<R.size()) S.push_back(R[j++]);
}
void merge_sort(int A[], int l, int r){
if(l<r){
int mid = l + (r-l)/2;
merge_sort(A, l, mid);
merge_sort(A, mid+1, r);
vector<int> L, R, S;
for(int i=l;i<=mid;i++) L.push_back(A[i]);
for(int i=mid+1;i<=r;i++) R.push_back(A[i]);
merge(L, R, S);
for(int i=0;i<S.size();i++) A[l+i] = S[i];
}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n;
cin>>n;
int A[n];
for(int i=0;i<n;i++) cin>>A[i];
merge_sort(A, 0, n-1);
cout<<ans;
return 0;
}