Submission #3441350

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Source Code Expand

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int N,B[100010];
typedef long long ll;
ll merge_count(vector<ll> &a){
	int n = a.size();
	if(n<=1) return 0;
	ll cnt = 0;
	vector<ll> b(a.begin(),a.begin() + n/2);
	vector<ll> c(a.begin() + n/2, a.end());
	cnt += merge_count(b);
	cnt += merge_count(c);
	int ai = 0,bi = 0,ci = 0;
	while(ai<n){
		if(bi<b.size() && (ci == c.size() || b[bi] <= c[ci])){
			a[ai++] = b[bi++];
		}else{
			cnt += n/2 - bi;
			a[ai++] = c[ci++];
		}
	}
	return cnt;
}

int main(){
	cin >> N;
	vector<pair<int,int>> v;
	vector<ll> u(N);
	for(int i=0;i<N;i++){
		cin >> B[i];
		v.push_back({B[i],i});
	}
	sort(v.begin(),v.end());
	int l = 0,r = N-1;
	for(int i=0;i<v.size();i++){
		int j = v[i].second;
		if(j-l>r-j){
			u[j] = r;
			r--;
		}else{
			u[j] = l;
			l++;
		}
	}
	cout << merge_count(u) << endl;
}

Submission Info

Judge Result