Submission #595076

#	Time	Username	Problem	Language	Result	Execution time	Memory
595076		elkernos	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	50 ms	5324 KiB

monochrome

#include <bits/stdc++.h>

using namespace std;

#define int long long

int32_t main()
{
    cin.tie(0)->sync_with_stdio(0);
    int n;
    cin >> n;
    vector<int> white, red;
    for(int i = 1; i <= 2 * n; i++) {
        char c;
        cin >> c;
        if(c == 'W') {
            white.emplace_back(i);
        }
        else {
            red.emplace_back(i);
        }
    }
    if(red[0] == 1) {
        swap(red, white);
    }
    int ans = 0;
    auto solve_for = [&](int k) {
        auto dist = [&](int i, int j) {
            int len = abs(j - i) - 1;
            return min(len, 2 * n - len - 2);
        };
        int cnt = 0;
        for(int i = 0; i < n; i++) {
            cnt += dist(white[i], red[(i + k) % n]);
        }
        ans = max(ans, cnt);
        return cnt;
    };
    int L = solve_for(0), R = solve_for(n - 1);
    if(L > R) {
        int l = 1, r = n - 2;
        while(l <= r) {
            int m = (l + r) / 2;
            int v1 = solve_for(m);
            if(v1 <= R) {
                r = m - 1;
                continue;
            }
            int v2 = solve_for(m + 1);
            if(v1 < v2) {
                l = m + 2;
            }
            else {
                r = m - 1;
            }
        }
    }
    else {
        int l = 1, r = n - 2;
        while(l <= r) {
            int m = (l + r) / 2;
            int v1 = solve_for(m);
            if(v1 <= L) {
                l = m + 1;
                continue;
            }
            int v2 = solve_for(m + 1);
            if(v1 < v2) {
                l = m + 2;
            }
            else {
                r = m - 1;
            }
        }
    }
    cout << ans / 2 << '\n';
}

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