Submission #299180

#	Time	Username	Problem	Language	Result	Execution time	Memory
299180		eriksuenderhauf	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	58 ms	15892 KiB

monochrome

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5 + 5;
int a[4*N], nxt[3*N][2];
int idx[4*N][2], vis[2*N];
vector<int> pos;

ll solve(int n, int i) {
  int ptr[2] = {i+n, i+n};
  ll val = 0;
  for (int j = i; j < i+n; ++j)
    val += min((ptr[a[j]] = nxt[ptr[a[j]]][a[j]] + 1) - n - i - 1, j - i);
  return val;
}

int main() {
  ios_base::sync_with_stdio(false); cin.tie(0);
  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';
  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;
  }
  idx[0][a[0]] = 1, idx[0][a[0]^1] = 0;
  for (int i = 1; i < 4*n; i++) {
    idx[i][0] = idx[i-1][0], idx[i][1] = idx[i-1][1];
    idx[i][a[i]]++;
  }
  auto bin = [&](ll& ans) {
    int lo = 0, hi = pos.size() - 1;
    while (lo <= hi) {
      int mi = (lo + hi) / 2;
      ll x1 = solve(n, pos[mi]);
      ans = max(ans, x1);
      if (lo == hi)
        break;
      if (x1 < solve(n, pos[mi+1]))
        lo = mi + 1;
      else
        hi = mi - 1;
    }
    // for (int i = max(0, hi - 20); i <= min((int)pos.size() - 1, lo + 20); i++)
    //   ans = max(ans, solve(n, pos[i]));
  };
  for (int i = n-1; i >= 0; i--) if (s[i] == s[i+n])
    if (a[i] == 0)
      vis[idx[nxt[i+n][a[i]]][a[i]^1] - idx[i][a[i]]] = i+1;
  ll ans = solve(n, 0);
  bin(ans);
  for (int i: pos)
    ans = max(ans, solve(n, i));
  pos.clear();
  for (int i = n-1; i >= 0; i--) if (s[i] == s[i+n])
    if (a[i] == 1)
      vis[idx[nxt[i+n][a[i]^1]][a[i]] - idx[nxt[i][a[i]]][a[i]^1]] = i+1;
  for (int i = 0; i < n; i++) if (vis[i])
    pos.push_back(vis[i] - 1);
  bin(ans);
  cout << ans << "\n";
}

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