Submission #397163

#	Time	Username	Problem	Language	Result	Execution time	Memory
397163		phathnv	Monochrome Points (JOI20_monochrome)	C++11	100 / 100	25 ms	3416 KiB

monochrome

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

int n;
string s;
vector<int> b, w;

ll Calc(int k){
    ll res = 0;
    int j = k;
    for(int i = 0; i < n; i++){
        int dist = abs(b[i] - w[j]);
        res += min(dist, 2 * n - dist);
        j = (j == n - 1? 0 : j + 1);
    }
    return res;
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> s;
    for(int i = 0; i < 2 * n; i++)
        if (s[i] == 'B')
            b.push_back(i);
        else
            w.push_back(i);
    ll a = Calc(0);
    ll b = Calc(n - 1);
    ll answer = max(a, b);
    int l = 1, r = n - 2;
    if (a > b){
        while (l <= r){
            int mid = (l + r) >> 1;
            ll val = Calc(mid);
            if (val <= b){
                r = mid - 1;
                continue;
            }
            ll val2 = Calc(mid + 1);
            if (val < val2){
                answer = max(answer, val2);
                l = mid + 2;
            } else {
                answer = max(answer, val);
                r = mid - 1;
            }
        }
    } else {
        while (l <= r){
            int mid = (l + r) >> 1;
            ll val = Calc(mid);
            if (val <= a){
                l = mid + 1;
                continue;
            }
            ll val2 = Calc(mid + 1);
            if (val < val2){
                answer = max(answer, val2);
                l = mid + 2;
            } else {
                answer = max(answer, val);
                r = mid - 1;
            }
        }
    }
    cout << (answer - n) / 2;
    return 0;
}

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