Submission #946393

#	Time	Username	Problem	Language	Result	Execution time	Memory
946393		efedmrlr	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	65 ms	8932 KiB

monochrome

// #pragma GCC optimize("O3,Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>

using namespace std;


#define int long long int
#define MP make_pair
#define pb push_back
#define REP(i,n) for(int i = 0; (i) < (n); (i)++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()


void fastio() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
}


const double EPS = 0.00001;
const int INF = 1e9+500;
const int N = 3e5+5;
const int ALPH = 26;
const int LGN = 25;
constexpr int MOD = 1e9+7;
int n,m,q;
vector<int> pw;
vector<int> b,w;
int getSum(int l, int r) {
    if(l <= r) {
        return pw[r] - ((l > 0) ? pw[l - 1] : 0);
    }
    return pw[r] + (pw[2*n-1] - ((l > 0) ? pw[l - 1] : 0));
}
int dif(int l, int r) {
    if(l <= r) return r - l + 1;
    else return 2*n + r - l + 1;
}
int calc_k(int k) {
    int ret = 0;
    for(int i = 0; i<n; i++) {
        int j = (i + k) % n;
        int wu = getSum(w[i], b[j]) - 1;
        int wd = n - 1 - wu, bu = dif(w[i], b[j]) - 2 - wu;
        int bd = n - 1 - bu;

        // cout << " wi:" << w[i] << " bj:" << b[j] << " wu:" << wu << " wd:" << wd << " bu:" << bu << " bd:" << bd <<  "\n";
        ret += min(wu, bd) + min(wd, bu);
    }
    // cout << ret << "\n";
    return ret / 2;
}
int ceil_div(int x, int y) {
    return (x - 1) / y + 1;
}
inline void solve() {
    cin >> n;
    string s;
    cin >> s;
    pw.assign(2*n + 3, 0);
    pw[0] = s[0] == 'W';
    for(int i = 0; i<2*n; i++) {
        if(s[i] == 'B') b.pb(i);
        else w.pb(i);
    }
    for(int i = 1; i<2*n; i++) {
        pw[i] = pw[i - 1] + (s[i] == 'W');
    }

    int tl = 0, tr = n - 1;
    while(tl < tr) {
        int tm1 = tl + (tr - tl) / 3;
        int tm2 = tl + ceil_div(2*(tr - tl), 3);
        if(calc_k(tm1) < calc_k(tm2)) {
            tl = tm1 + 1;
        }
        else {
            tr = tm2 - 1;
        }
    }
    cout << calc_k(tl) << "\n";
}
 
signed main() {

    fastio();
    int test = 1;
    //cin>>test;
    while(test--) {
        solve();
    }
    
}

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