Submission #710614

#	Time	Username	Problem	Language	Result	Execution time	Memory
710614		KoD	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	43 ms	1996 KiB

monochrome

#include <algorithm>
#include <bits/stdc++.h>
using namespace std;
using ll = long long;

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

    int N;
    cin >> N;
    vector<int> W, B;
    W.reserve(N);
    B.reserve(N);
    for (int i = 0; i < 2 * N; ++i) {
        char c;
        cin >> c;
        (c == 'W' ? W : B).push_back(i);
    }

    auto f = [&](int k) {
        ll ret = 0;
        for (int i = 0; i < N; ++i) {
            int j = i + k;
            if (j >= N) j -= N;
            int d = abs(W[i] - B[j]);  
            ret += min(d - 1, 2 * N - 1 - d);
        }
        return ret / 2;
    };

    int l = 0, r = N - 1;
    while (r - l > 5) {
        const int x1 = (l + l + r) / 3;
        const int x2 = (l + r + r) / 3;
        if (f(x1) < f(x2)) {
            l = x1;
        } else {
            r = x2;
        }
    }
    ll ans = 0;
    for (int k = l; k <= r; ++k) {
        ans = max(ans, f(k));
    }
    cout << ans << '\n';

    return 0;
}

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