Submission #1042767

#	Time	Username	Problem	Language	Result	Execution time	Memory
1042767		abczz	Chorus (JOI23_chorus)	C++17	100 / 100	1760 ms	63960 KiB

chorus

#include <iostream>
#include <algorithm>
#include <deque>
#include <vector>
#include <array>
#include <cmath>
#define ll long long
#define ld long double

using namespace std;

ll n, k, l, r, mid, dp[1000000];
ll tot[1000000];
ld ep = 1e-8;
vector <ll> A, B, nxA, ps;
string S, T;
struct Line{
  ll m; 
  ll c;
  ll x;
};
ld intx(Line I, Line J) {
  return (ld)(I.c-J.c)/(J.m-I.m);
}
ll C(ll l, ll r) {
  if (nxA[l] > r) return 0;
  ll nx = max(l, nxA[l]), cnt = r-nx+1, cnt2 = max(0LL, l-nxA[l]);
  return ps[r]-(nx ? ps[nx-1] : 0)-cnt*B[l]-cnt*(cnt-1)/2-(r-l+1)*cnt2;
}

ll f(ll i) {
  ll nx = max(i, nxA[i]), cnt2 = max(0LL, i-nxA[i]);
  return -(nx ? ps[nx-1] : 0)+nx*B[i]-B[i] + (-nx*nx+nx)/2 + cnt2*i - cnt2;
}

ll g(ll j) {
  return ps[j] + (-j*j-j)/2;
}

ll h(ll i) {
  return nxA[i]-B[i];
}

void solve() {
  deque <Line> dq;
  dq.push_back({h(0), f(0), 0});
  for (ll i=0; i<n; ++i) {
    while (dq.size() > 1) {
      auto I = dq.front();
      dq.pop_front();
      auto J = dq.front();
      if ((ld)i-intx(I, J) > ep || fabs((ld)i-intx(I, J)) <= ep) continue;
      else {
        dq.push_front(I);
        break;
      }
    }
    auto X = dq.front();
    dp[i] = X.m * i + X.c + g(i) + mid;
    tot[i] = X.x+1;
    if (i != n-1) {
      Line K = {h(i+1), dp[i] + f(i+1), tot[i]};
      while (dq.size() > 1) {
        auto J = dq.back();
        dq.pop_back();
        auto I = dq.back();
        if (intx(I, J)-intx(I, K) > ep || fabs(intx(I, J)-intx(I, K)) <= ep) continue;
        else {
          dq.push_back(J);
          break;
        }
      }
      dq.push_back(K);
    }
  }
}


int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cin >> n >> k >> S;
  for (int i=0; i<2*n; ++i) {
    if (S[i] == 'A') {
      ps.push_back((ps.empty() ? 0 : ps.back()) + i);
      A.push_back(i);
    }
    else {
      B.push_back(i);
      nxA.push_back(A.size());
    }
  }
  l = 0, r = n*n;
  while (l < r) {
    mid = (l+r+1)/2;
    solve();
    if (k > tot[n-1]) r = mid-1;
    else l = mid;
  }
  mid = l;
  solve();
  cout << dp[n-1] - k * mid << '\n';
}

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