Submission #710597

#	Time	Username	Problem	Language	Result	Execution time	Memory
710597		KoD	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	29 ms	2276 KiB

monochrome

#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 = -1, r = N;
    while (r - l > 2) {
        const int x1 = (l + r) / 2;
        const int x2 = x1 + 1;
        if (f(x1) < f(x2)) {
            l = x1;
        } else {
            r = x2;
        }
    }
    cout << f(l + 1) << '\n';

    // int min = -1, max = N;
    // int s = 1, t = 2;
    // while (min + t < max) swap(s += t, t);
    // int a = min, b = min + t, x = min + s;
    // ll fx = f(x), fy;
    // while (a + b != 2 * x) {
    //     int y = a + b - x;
    //     if (y < max and fx < (fy = f(y))) {
    //         fx = fy;
    //         b = x;
    //         x = y;
    //     } else {
    //         a = b;
    //         b = y;
    //     }
    // }
    // cout << fx << '\n';

    return 0;
}

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