Submission #411575

#	Time	Username	Problem	Language	Result	Execution time	Memory
411575		nichke	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	1229 ms	14884 KiB

monochrome

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'

int ans;
int n;
string s;

vector<int> a, b;
int bit[400005];

void clr() {
	for (int i = 1; i <= 2 * n; i++) {
		bit[i] = 0;
	}
}

void upd(int v, int k) {
	while (v <= 2 * n) {
		bit[v] += k;
		v += (v & (-v));
	}
}

int qry(int v) {
	int res = 0;
	while (v) {
		res += bit[v];
		v -= (v & (-v));
	}
	return res;
}

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

int calc(int k) {
	int res = 0;
	vector<pair<int, int>> v;
	for (int i = 0; i < n; i++) {
		v.push_back({a[i], b[(i + k) % n]});
	}
	for (int i = 0; i < v.size(); i++) {
		if (v[i].first > v[i].second) {
			swap(v[i].first, v[i].second);
		}
	}
	sort(v.begin(), v.end());
	clr();
	for (int i = 0; i < v.size(); i++) {
		res += sum(v[i].first, v[i].second);
		upd(v[i].second, 1);
	}
	return res;
}

signed main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin >> n >> s;
	for (int i = 0; i < 2 * n; i++) {
		if (s[i] == 'W') {
			a.push_back(i + 1);
		} else {
			b.push_back(i + 1);
		}
	}
	ans = max(calc(0), calc(n - 1));
	int l = 0, r = n - 2;
	while (l <= r) {
		int m = (l + r) / 2;
		int a = calc(m);
		int b = calc(m + 1);
		ans = max(ans, max(a, b));
		if (a < b) {
			l = m + 1;
		} else {
			r = m - 1;
		}
	}
	cout << ans << '\n';
	return 0;
}

Compilation message (stderr)

monochrome.cpp: In function 'long long int calc(long long int)':
monochrome.cpp:45:20: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |  for (int i = 0; i < v.size(); i++) {
      |                  ~~^~~~~~~~~~
monochrome.cpp:52:20: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   52 |  for (int i = 0; i < v.size(); i++) {
      |                  ~~^~~~~~~~~~

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