Submission #311802

#	Time	Username	Problem	Language	Result	Execution time	Memory
311802		MarcoMeijer	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	77 ms	9612 KiB

monochrome

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

// macros
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define FOR(a,b) for(auto& a : b)
#define all(a) a.begin(), a.end()
#define INF 1e9
#define EPS 1e-9
#define pb push_back
#define popb pop_back
#define fi first
#define se second
#define sz size()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

// input
template<class T> void IN(T& x) {cin >> x;}
template<class H, class... T> void IN(H& h, T&... t) {IN(h); IN(t...); }

// output
template<class T1, class T2> void OUT(const pair<T1,T2>& x);
template<class T> void OUT(const T& x) {cout << x;}
template<class H, class... T> void OUT(const H& h, const T&... t) {OUT(h); OUT(t...); }
template<class T1, class T2> void OUT(const pair<T1,T2>& x) {OUT(x.fi,' ',x.se);}
template<class... T> void OUTL(const T&... t) {OUT(t..., "\n"); }
template<class H> void OUTLS(const H& h) {OUTL(h); }
template<class H, class... T> void OUTLS(const H& h, const T&... t) {OUT(h,' '); OUTLS(t...); }

//===================//
//  Added libraries  //
//===================//

//===================//
//end added libraries//
//===================//

void program();
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    program();
}


//===================//
//   begin program   //
//===================//

const int MX = 1e6;

int n;
string s;
int a[MX][2], N[2];
int cnt[MX][2];

ll getAns(int x) {
    ll ans = 0;
    RE(i,n) {
        int bp = a[i][0];
        int wp = a[(x+i)%n][1];
        if(wp < bp) wp += 2*n;
        int cntB = cnt[wp][0]-cnt[bp+1][0];
        int cntW = cnt[wp][1]-cnt[bp+1][1];
        ans += min(cntB, n-1-cntW);
        ans += min(cntW, n-1-cntB);
    }
    ans /= 2;
    return ans;
}

void program() {
    IN(n, s);
    s += s;
    RE(i,n*4) s[i] = (s[i] == 'B' ? 0 : 1);

    RE(i,2) N[i] = 0;
    RE(i,n*2) a[N[s[i]]++][s[i]] = i;
    cnt[0][0] = 0;
    cnt[0][1] = 0;
    RE(i,n*4) {
        RE(j,2) cnt[i+1][j] = cnt[i][j];
        cnt[i+1][s[i]]++;
    }

    if(n > 2000) {
        int lb=-1, ub=-1;
        while(lb == -1) {
            int i = rng()%n;
            if(getAns(i) < getAns((i+1)%n)) lb = i;
        }
        while(ub == -1) {
            int i = rng()%n;
            if(getAns(i) > getAns((i+1)%n)) ub = i;
        }
        if(ub < lb) ub += n;
        while(lb != ub) {
            int mid=(lb+ub)/2;
            if(getAns(mid%n)<getAns(mid+1)) lb=mid+1;
            else ub=mid;
        }
        OUTL(getAns(lb%n));
    } else {
        ll ans = 0;
        RE(i,n) ans = max(ans, getAns(i));
        OUTL(ans);
    }
}

Compilation message (stderr)

monochrome.cpp: In function 'void program()':
monochrome.cpp:93:23: warning: array subscript has type 'char' [-Wchar-subscripts]
   93 |     RE(i,n*2) a[N[s[i]]++][s[i]] = i;
      |                       ^
monochrome.cpp:93:32: warning: array subscript has type 'char' [-Wchar-subscripts]
   93 |     RE(i,n*2) a[N[s[i]]++][s[i]] = i;
      |                                ^
monochrome.cpp:98:22: warning: array subscript has type 'char' [-Wchar-subscripts]
   98 |         cnt[i+1][s[i]]++;
      |                      ^

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