Submission #683891

#	Time	Username	Problem	Language	Result	Execution time	Memory
683891		abc864197532	Monochrome Points (JOI20_monochrome)	C++17	35 / 100	2071 ms	2376 KiB

monochrome

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define pii pair<int,int>
#define all(x) x.begin(), x.end()

int main() {
	ios::sync_with_stdio(false), cin.tie(0);
	int n;
	string s;
	cin >> n >> s;
	vector <pii> a;
	for (int i = 0; i < n; ++i) {
		if (s[i] == s[i + n]) {
			a.emplace_back(i, s[i] == 'B' ? 1 : 0);
		}
	}
	int m = a.size();
	ll ans = 1ll << 60;
	if (!m) {
		cout << 1ll * n * (n - 1) / 2 << '\n';
		return 0;
	}
	for (int rt = 0; rt < m; ++rt) {
		vector <pii> stk;
		ll cur = 0;
		for (int i = 0; i < m; ++i) {
			auto [x, id] = a[(i + rt) % m];
			if (!stk.empty() && stk.back().second != id) {
				int p = stk.back().first; stk.pop_back();
				int len = abs(p - x);
				cur += min(len, n - len);
			} else {
				stk.emplace_back(x, id);
			}
		}
		ans = min(ans, cur);
	}
	cout << 1ll * n * (n - 1) / 2 - ans << '\n';
}

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