Submission #1145273

#	Time	Username	Problem	Language	Result	Execution time	Memory
1145273		guagua0407	Monochrome Points (JOI20_monochrome)	C++20	35 / 100	1248 ms	12392 KiB

monochrome

//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define f first
#define s second
#define all(x) x.begin(),x.end()
#define _ ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

int dx[4]={0,0,1,-1};
int dy[4]={1,-1,0,0};

void setIO(string s) {
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}

const int mxn=4e5+5;
int bit[mxn];

void update(int pos,int val){
    for(;pos<mxn;pos+=(pos&-pos)){
        bit[pos]+=val;
    }
}

int query(int pos){
    int ans=0;
    for(;pos>0;pos-=(pos&-pos)){
        ans+=bit[pos];
    }
    return ans;
}

int main() {_
    int n;
    cin>>n;
    vector<int> a,b;
    for(int i=1;i<=2*n;i++){
        char c;
        cin>>c;
        if(c=='B') a.push_back(i);
        else b.push_back(i);
    }
    bool tf=false;
    function<ll(int)> get=[&](int k){
        k=(k+n)%n;
        if(tf) k=n-k-1;
        vector<pair<int,int>> p;
        for(int i=0;i<n;i++){
            p.push_back({a[i],b[(i+k)%n]});
        }
        for(auto &v:p){
            if(v.s<v.f) swap(v.f,v.s);
        }
        vector<pair<int,int>> vec;
        for(int i=0;i<n;i++){
            vec.push_back({p[i].f,-1});
            vec.push_back({p[i].s,i});
        }
        sort(all(vec));
        ll ans=0;
        memset(bit,0,sizeof(bit));
        for(auto v:vec){
            auto [pos,id]=v;
            if(id<0){
                ans-=query(pos);
            }
            else{
                ans+=query(p[id].f);
                update(p[id].f,1);
            }
        }
        return ans;
    };
    if(get(0)>get(1)){
        tf=true;
    }
    int l=0,r=n-1;
    int val=get(0);
    while(l<r){
        int mid=(l+r)/2;
        int v1=get(mid);
        int v2=get(mid+1);
        if(v1>v2){
            r=mid;
        }
        else{
            if(v1>=val){
                l=mid+1;
            }
            else{
                r=mid-1;
            }
        }
    }
    cout<<max({get(l-1),get(l),get(l+1)})<<'\n';
    return 0;
}
//maybe its multiset not set
//yeeorz
//diaoborz

Compilation message (stderr)

monochrome.cpp: In function 'void setIO(std::string)':
monochrome.cpp:15:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   15 |     freopen((s + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
monochrome.cpp:16:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   16 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 4 / 4
• Subtask 2: 21 / 21
• Subtask 3: 10 / 10
• Subtask 4: 0 / 65