Submission #864479

#	Time	Username	Problem	Language	Result	Execution time	Memory
864479		HuyQuang_re_Zero	Islands (IOI08_islands)	C++14	80 / 100	553 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];
struct edge { int u,v,k; };
edge e[N];
int tr[N],trc[N],cycle[N];
bool incycle[N],visited[N];
ll n,i,u,v,k,c[N],dis[N],ncycle,sum,res;
const ll oo=round(1e18);
struct Fenwick_Tree
{
    ll bit[N],d[N],n;
    void Init(int _n)
    {
        n=_n;
        for(int i=1;i<=n;i++) bit[i]=d[i]=-oo;
    }
    void update(int i,ll k)
    {
        d[i]=max(d[i],k);
        while(i<=n) bit[i]=max(bit[i],k),i+=(i & -i);
    }
    ll get(int l,int r)
    {
        ll res=-oo,i=r;
        while(i>=l)
            if(i-(i & -i)>=l) res=max(res,bit[i]),i-=(i & -i);
            else res=max(res,d[i]),i--;
        return res;
    }
} FT;

void dfs(int u)
{
    visited[u]=1;
    for(int adj:a[u])
    {
        int v=(e[adj].u==u ? e[adj].v : e[adj].u);
        if(visited[v]==0) dfs(v);
    }
}

void Find_cycle(int u,int x)
{
    for(int adj:a[u])
    {
        if(adj==x) continue;
        int v=v=(e[adj].u==u ? e[adj].v : e[adj].u),k=e[adj].k;
        if(tr[v]==0)
        {
            tr[v]=u; trc[v]=k;
            Find_cycle(v,adj);
        }
        else if(ncycle==0)
        {
            sum=0;
            while(u!=v)
            {
                cycle[++ncycle]=u; incycle[u]=1;
                dis[ncycle]=sum; sum+=trc[u];
                u=tr[u];
            }
            cycle[++ncycle]=u; incycle[u]=1;
            dis[ncycle]=sum; sum+=k;
            return ;
        }
    }
}


/////////////////////////////////////////////////////////////////////////////
ll cal(int u,int p,ll &ma)
{
    ll res=0,ma0=0,ma1=0;
    for(int adj:a[u])
    {
        int v=v=(e[adj].u==u ? e[adj].v : e[adj].u);;
        if(v!=p && incycle[v]==0)
        {
            ll k=cal(v,u,ma)+e[adj].k;
            res=max(res,k);
            if(ma0<k) ma0=k;
            if(ma1<ma0) swap(ma1,ma0);
        }
    }
    ma=max(ma,ma0+ma1);
    return res;
}
ll Work()
{
    int i,u,v;
    FT.Init(ncycle);
    ll res=0;
    for(i=1;i<=ncycle;i++)
    {
        u=cycle[i];
        c[i]=cal(u,0,res);
        FT.update(i,c[i]-dis[i]);
    }
    for(i=1;i<ncycle;i++)
    {
        int l=i,r=ncycle;
        while(l<r)
        {
            int mid=(l+r+1)>>1;
            if(sum-(dis[mid]-dis[i])>=dis[mid]-dis[i])
                l=mid;
            else r=mid-1;
        }
        res=max(res,c[i]+sum+dis[i]+FT.get(i+1,l));
    }

    FT.Init(ncycle);
    for(i=1;i<=ncycle;i++)
    {
        u=cycle[i];
        FT.update(i,c[i]+dis[i]);
    }
    for(i=1;i<ncycle;i++)
    {
        int l=i,r=ncycle;
        while(l<r)
        {
            int mid=(l+r+1)>>1;
            if(sum-(dis[mid]-dis[i])>=dis[mid]-dis[i])
                l=mid;
            else r=mid-1;
        }
        res=max(res,c[i]-dis[i]+FT.get(l+1,ncycle));
    }
    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;
        a[u].push_back(u); a[v].push_back(u);
        e[u]={ u,v,k };
    }
    for(u=1;u<=n;u++)
        if(visited[u]==0)
        {
            dfs(u);
            tr[u]=-1;
            ncycle=0;
            Find_cycle(u,0);
            res+=Work();
        }
    cout<<res;
}

Compilation message (stderr)

islands.cpp: In function 'void Find_cycle(int, int)':
islands.cpp:62:16: warning: operation on 'v' may be undefined [-Wsequence-point]
   62 |         int v=v=(e[adj].u==u ? e[adj].v : e[adj].u),k=e[adj].k;
      |               ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
islands.cpp: In function 'long long int cal(int, int, long long int&)':
islands.cpp:91:16: warning: operation on 'v' may be undefined [-Wsequence-point]
   91 |         int v=v=(e[adj].u==u ? e[adj].v : e[adj].u);;
      |               ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
islands.cpp: In function 'long long int Work()':
islands.cpp:105:13: warning: unused variable 'v' [-Wunused-variable]
  105 |     int i,u,v;
      |             ^
islands.cpp: In function 'int main()':
islands.cpp:158:16: warning: narrowing conversion of 'u' from 'long long int' to 'int' [-Wnarrowing]
  158 |         e[u]={ u,v,k };
      |                ^
islands.cpp:158:18: warning: narrowing conversion of 'v' from 'long long int' to 'int' [-Wnarrowing]
  158 |         e[u]={ u,v,k };
      |                  ^
islands.cpp:158:20: warning: narrowing conversion of 'k' from 'long long int' to 'int' [-Wnarrowing]
  158 |         e[u]={ u,v,k };
      |                    ^

• 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: 0 / 10
• Subtask 9: 0 / 10