Submission #1031443

#	Time	Username	Problem	Language	Result	Execution time	Memory
1031443		Unforgettablepl	Chorus (JOI23_chorus)	C++17	40 / 100	7018 ms	836 KiB

chorus

#pragma GCC optimize("Ofast","unroll-loops")
#include <bits/stdc++.h>
using namespace std;
 
#define int long long
 
const int INF = 1e18;
 
struct fenwick{
	vector<int> tree;
	int n;
	fenwick(int n):n(n),tree(n+1){}
	void add(int k,int x){
		while(k<=n){
			tree[k]+=x;
			k+=k&-k;
		}
	}
	void reset(){
		fill(tree.begin(),tree.end(),0ll);
	}
	int get(int k){
		int ans = 0;
		while(k){
			ans+=tree[k];
			k-=k&-k;
		}
		return ans;
	}
};
 
int32_t main(){
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	int n,k;
	cin >> n >> k;
	string s;
	cin >> s;
	s.insert(s.begin(),'$');
	vector<int> posA(n+1);
	vector<int> posB(n+1);
	int cntA = 0,cntB = 0;
	for(int i=1;i<=2*n;i++){
		if(s[i]=='A'){
			posA[++cntA]=i;
		} else {
			posB[++cntB]=i;
		}
	}
	fenwick addedA(2*n);
	fenwick addedB(2*n);
	auto solve = [&](int penalty){
		vector<pair<int,int>> DP1(n+1,{INF,-INF});
		vector<pair<int,int>> DP2(n+1,{INF,-INF});
		DP1[0]={0,0};
		DP2[0]={0,0};
		for(int i=1;i<=n;i++){
			int ans = penalty;
			addedA.reset();
			addedB.reset();
			for(int j=i+1;j<=n;j++)addedB.add(posB[j],1);
			for(int j=i;j;j--){
				ans+=i-j-addedA.get(posB[j]);
				addedB.add(posB[j],1);
				ans+=addedB.get(posA[j]);
				addedA.add(posA[j],1);
				DP1[i]=min(DP1[i],{DP1[j-1].first+ans,DP1[j-1].second-1});
				DP2[i]=min(DP2[i],{DP2[j-1].first+ans,DP2[j-1].second+1});
			}
		}
		DP1[n].second*=-1ll;
		auto mini = DP2[n];
		auto maxi = DP1[n];
		if(mini.second>k)return mini;
		if(maxi.second<=k)return maxi;
		return make_pair(mini.first,k);
	};
	int best_penalty = -1;
	for(int jump=(1ll<<40);jump;jump/=2ll){
		if(solve(best_penalty+jump).second>k)best_penalty+=jump;
	}
	// for(int i=0;i<=10;i++)cout<<solve(i).second<<'\n';
	best_penalty++;
	cout << solve(best_penalty).first-solve(best_penalty).second*best_penalty << '\n';
}

Compilation message (stderr)

chorus.cpp: In constructor 'fenwick::fenwick(long long int)':
chorus.cpp:11:6: warning: 'fenwick::n' will be initialized after [-Wreorder]
   11 |  int n;
      |      ^
chorus.cpp:10:14: warning:   'std::vector<long long int> fenwick::tree' [-Wreorder]
   10 |  vector<int> tree;
      |              ^~~~
chorus.cpp:12:2: warning:   when initialized here [-Wreorder]
   12 |  fenwick(int n):n(n),tree(n+1){}
      |  ^~~~~~~

• Subtask 1: 16 / 16
• Subtask 2: 24 / 24
• Subtask 3: 0 / 21
• Subtask 4: 0 / 26
• Subtask 5: 0 / 13