Submission #864502

#	Time	Username	Problem	Language	Result	Execution time	Memory
864502		HuyQuang_re_Zero	Islands (IOI08_islands)	C++14	90 / 100	828 ms	131072 KiB

islands

#include <bits/stdc++.h>
#define ll long long
#define db long double
#define N 1000005
#define II pair <int,int>
#define III pair <ll,II>
#define IV pair <vector <int>,vector <int> >
#define fst first
#define snd second
#define BIT(x,i) ((x>>i)&1)
#define Log(x) (31-__builtin_clz((int)x))
#define LogLL(x) (63-__builtin_clzll((ll)x))
#define pi acos(-1)
#define to_radian(x) (x*pi/180.0)
#define to_degree(x) (x*180.0/pi)
using namespace std;
vector <int> a[N];
int tr[N],trc[N],nxt[N],w[N];
bool incycle[N],visited[N];
ll n,i,u,v,k,ncycle,sum,res;
vector <ll> dis,c;
const ll oo=round(1e18);

void dfs(int u)
{
    visited[u]=1;
    auto consider=[&](int v)
    {
        if(visited[v]==0) dfs(v);
    };
    for(int adj:a[u]) consider(adj);
    consider(nxt[u]);
}

void Find_cycle(int u,int x)
{
    auto consider=[&](int v,int From)
    {
        if(From==x) return;
        int k=w[From];
        if(tr[v]==0)
        {
            tr[v]=u; trc[v]=k;
            Find_cycle(v,From);
        }
        else if(ncycle==0)
        {
            sum=0;
            while(u!=v)
            {
                ncycle++;
                c.push_back(u); incycle[u]=1;
                dis.push_back(sum); sum+=trc[u];
                u=tr[u];
            }
            ncycle++;
            c.push_back(u); incycle[u]=1;
            dis.push_back(sum); sum+=k;
            return ;
        }
    };
    for(int adj:a[u])
    {
        consider(adj,adj);
        if(ncycle>0) return ;
    }
    consider(nxt[u],u);
}


/////////////////////////////////////////////////////////////////////////////
ll cal(int u,int p,ll &ma)
{
    ll res=0,ma0=0,ma1=0;
    auto consider=[&](int adj,int From)
    {
        int v=adj;
        if(v!=p && incycle[v]==0)
        {
            ll k=cal(v,u,ma)+w[From];
            res=max(res,k);
            if(ma0<k) ma0=k;
            if(ma1<ma0) swap(ma1,ma0);
        }
    };
    for(int adj:a[u]) consider(adj,adj);
    consider(nxt[u],u);
    ma=max(ma,ma0+ma1);
    return res;
}
ll Work()
{
    int i,u,v;
    ll res=0,ma=-oo;
    for(i=1;i<=ncycle;i++)
    {
        u=c[i];
        c[i]=cal(u,0,res);
    }
    deque <int> dq;
    int j=1;
    for(i=1;i<ncycle;i++)
    {
        while(j<ncycle && sum-dis[j+1]+dis[i]>=dis[j+1]-dis[i])
        {
            j++;
            while(dq.size()>0 && c[dq.back()]-dis[dq.back()]<c[j]-dis[j])
                dq.pop_back();
            dq.push_back(j);
        }
        if(dq.size()>0 && dq.front()==i) dq.pop_front();
        if(dq.size()>0) res=max(res,c[i]+c[dq.front()]+sum+dis[i]-dis[dq.front()]);
    }

    j=ncycle+1;
    for(i=ncycle-1;i>=1;i--)
    {
        while(j-1>i && sum-dis[j-1]+dis[i]<dis[j-1]-dis[i])
        {
            j--;
            ma=max(ma,c[j]+dis[j]);
        }
        res=max(res,c[i]-dis[i]+ma);
    }
    return res;
}
int main()
{
 //   freopen("islands.inp","r",stdin);
  //  freopen("islands.out","w",stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    cin>>n;
    for(u=1;u<=n;u++)
    {
        cin>>v>>k;
        nxt[u]=v; a[v].push_back(u);
        w[u]=k;
    }
    for(u=1;u<=n;u++)
        if(visited[u]==0)
        {
            dfs(u);
            tr[u]=-1;
            ncycle=0;
            c.clear(); c.push_back(0);
            dis.clear(); dis.push_back(0);
            Find_cycle(u,0);
            res+=Work();
        }
    cout<<res;
}

Compilation message (stderr)

islands.cpp: In function 'long long int Work()':
islands.cpp:93:13: warning: unused variable 'v' [-Wunused-variable]
   93 |     int i,u,v;
      |             ^

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 0 / 10