Submission #298165

#	Time	Username	Problem	Language	Result	Execution time	Memory
298165		eriksuenderhauf	Monochrome Points (JOI20_monochrome)	C++17	35 / 100	16 ms	10260 KiB

monochrome

#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("avx2")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5 + 5;
int a[4*N], nxt[3*N][2];
ll dp[N];
int ord[2*N];
 
ll solve(int n, int i) {
  i = ord[i];
  int ptr[2] = {i+n, i+n}, cnt[4] = {0, 0, 0, 0};
  // auto next = [&](int& j) {
  //   j = j+1 < 2*n ? j+1 : j+1-2*n;
  // };
  // #define next(x) x = x+1 < 2*n ? x+1 : x+1-2*n
  ll val = 0;
  for (int j = i, c = a[i]; j < i+n; c = a[++j]) {
    cnt[c+2] += nxt[ptr[c]][c] - ptr[c];
    ptr[c] = nxt[ptr[c]][c] + 1;
    val += min(cnt[c+2], cnt[c^1]) + cnt[c]++;
  }
  return val;
}
 
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

int main() {
  ios_base::sync_with_stdio(false); cin.tie(0);
  auto cur_t = clock();
  int n; cin >> n;
  string s; cin >> s;
  for (int i = 0; i < 2*n; i++)
    a[i] = a[i+2*n] = s[i] == 'B', ord[i] = i;
  nxt[3*n][0] = nxt[3*n][1] = 3*n;
  for (int i = 3*n-1; i >= 0; i--) {
    nxt[i][0] = nxt[i+1][0], nxt[i][1] = nxt[i+1][1];
    nxt[i][a[i]^1] = i;
  }
  shuffle(ord, ord+n, rng);
  ll ans = 0;
  int i = 0;
  while (clock() - cur_t < 1993)
    ans = max(ans, i < n ? solve(n, i++) : 0);
  cout << ans << "\n";
}

• Subtask 1: 4 / 4
• Subtask 2: 21 / 21
• Subtask 3: 10 / 10
• Subtask 4: 0 / 65