Submission #855276

#	Time	Username	Problem	Language	Result	Execution time	Memory
855276		willychan	Chorus (JOI23_chorus)	C++14	40 / 100	7085 ms	604 KiB

chorus

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
//#include<bits/extc++.h>
//__gnu_pbds
const int N = 5005;
pair<ll,int> dp[N];
int Bpa[N];
ll Bpasum[N];
int n,K;

ll cost(int i,int j){
	int l = i;
	int r = j+1;
	while(r-l>1){
		int mid = (l+r)/2;
		if(Bpa[mid]<j) l = mid;
		else r = mid;
	}
	int cnt = l-i;
	ll ans = Bpasum[l]-Bpasum[i];
	return cnt*j-ans;	
}

bool ok(int v){
	for(int i=0;i<=n;i++) dp[i] = {1e18,0};
	dp[0]={0,0};
	for(int i=1;i<=n;i++){
		for(int j=1;j<=i;j++){
			dp[i] = min({dp[i-j].first+cost(i-j,i)+v,dp[i-j].second+1},dp[i]);
		}
	}
	//cout<<(dp[n].second<=K)<<" "<<dp[n].first<<" "<<v<<"\n";
	return (dp[n].second<=K);
}
 
int main(){
	ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	cin>>n>>K;			
	string s;cin>>s;
	int pa = 0;
	int pb = 0;
	for(int i=1;i<=2*n;i++){
		if(s[i-1]=='A') pa++;
		if(s[i-1]=='B') Bpa[++pb]=pa;
	}
	for(int i=1;i<=n;i++){
		Bpasum[i] = Bpasum[i-1]+Bpa[i];
	}
	ll l = -1;ll r = 1e9;
	while(r-l>1){
		ll mid = l+((r-l)/2);
		if(ok(mid)) r = mid;
		else l = mid;
	}
	ok(r);
	//cout<<r<<"\n";
	cout<<dp[n].first-r*K<<"\n";
 
	return 0;
}

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