Submission #299303

#	Time	Username	Problem	Language	Result	Execution time	Memory
299303		eriksuenderhauf	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	57 ms	15764 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]]++;
  }
  ll ans = solve(n, 0);
  for (int i = 0; i < n; i++) if (s[i] == s[i+n] && !a[i])
    vis[idx[nxt[i+n][0]][1] - idx[i][0]] = i+1;
  for (int i = 0; i < n; i++) if (s[i] == s[i+n] && a[i])
    vis[idx[nxt[i+n][0]][1] - idx[nxt[i][1]][0]] = i+1;
  for (int i = 0; i < n; i++) if (vis[i])
    pos.push_back(vis[i] - 1);
  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;
  }
  cout << ans << "\n";
}

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