Submission #1239453

#	Time	Username	Problem	Language	Result	Execution time	Memory
1239453		trantrungkein	Monochrome Points (JOI20_monochrome)	C++20	100 / 100	834 ms	14324 KiB

monochrome

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 4e5 + 6;
string s; int n,bi = 0, wi = 0, b[N],w[N],BIT[N];
void update(int id)
{
    for(;id <= 2*n; id += (-id)&id) BIT[id] += 1;
}
int sum(int id)
{
    int res = 0;
    for(;id > 0; id -= (-id)&id) res += BIT[id];
    return res;
}
int get(int l, int r)
{
    return (sum(r) - sum(l-1));
}
int cal(int k)
{
    vector<pair<int,int>> edge;
    memset(BIT,0,sizeof(BIT));
    for(int i = 0; i < n; i++)
    {
        int c = min(w[i],b[(i+k)%n]) , d = max(w[i],b[(i+k)%n]);
        edge.push_back({c,d});
    }
    sort(edge.begin(),edge.end());
    int res = 0;
    for(auto [l,r] : edge)
    {
        //cout << l+1 <<' ' << r+1 << endl;
        res += get(l+1,r+1);
        update(r+1);
    }
   // cout << endl;
    //cout << res;
    return res;
}
 main()
{

    cin >> n >> s;
    for(int i = 0; i < 2*n; i++)
    {
        if(s[i] == 'W') w[wi++] = i;
        else b[bi++] = i;
    }
    //cout << cal(0) << endl;
    int l = 0, r = n-1, ans = 0;
    while(l <= r)
    {
        int mid = (l+r)/2;
        int curr = cal(mid);
        int prev = 0;
       // cout << l <<' ' << r << ' ' << mid << endl;
        if(mid - 1 >= 0)
        {
            prev = cal(mid-1);
        }
        ans = max(ans,curr);
        if(prev >= curr)
        {
            r = mid - 1;
        }
        else l = mid + 1;
    }
    ans = max(ans,cal(0));
    ans = max(ans,cal(n-1));
    cout << ans;
}

Compilation message (stderr)

monochrome.cpp:41:2: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   41 |  main()
      |  ^~~~

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