Submission #1043217

#	Time	Username	Problem	Language	Result	Execution time	Memory
1043217		juicy	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	961 ms	7844 KiB

monochrome

// sorry didnt tryin to prove:(

#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif

const int N = 2e5 + 5;

int n;
int ft[2 * N];
string s;
vector<int> W, B;

void upd(int i, int x) {
  for (; i <= 2 * n; i += i & -i) {
    ft[i] += x;
  }
}

int qry(int i) {
  int res = 0;
  for (; i; i -= i & -i) {
    res += ft[i];
  }
  return res;
}

int qry(int l, int r) {
  return qry(r) - qry(l - 1);
}

long long get(int k) {
  long long res = 0;
  vector<array<int, 2>> cands;
  for (int i = 0; i < n; ++i) {
    int a = W[i], b = B[(i + k) % n];
    cands.push_back({min(a, b), max(a, b)});
  }
  sort(cands.begin(), cands.end());
  fill(ft + 1, ft + 2 * n + 1, 0);
  for (auto [l, r] : cands) {
    res += qry(l, r);
    upd(r, 1);
  }
  return res;
}

int main() {
  ios::sync_with_stdio(false); cin.tie(nullptr);

  cin >> n;
  for (int i = 1; i <= 2 * n; ++i) {
    char c; cin >> c;
    (c == 'W' ? W : B).push_back(i);
  }
  int l = 1, r = n, p = 0;
  while (l <= r) {
    int md = (l + r) / 2;
    if (get(md - 1) <= get(md)) {
      p = md;
      l = md + 1;
    } else {
      r = md - 1;
    }
  }
  cout << get(p);
  return 0;
}

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