Submission #588738

#	Time	Username	Problem	Language	Result	Execution time	Memory
588738		Bench0310	Islands (IOI08_islands)	C++17	100 / 100	790 ms	131072 KiB

islands

#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

const int N=1000001;
int u[N];
int vidx[N];
ll dp[N];
ll down[N];
array<int,3> v[2*N];
int vsz=0;
int badidx=2*N;
int cycle[N];
int cyclesz=0;
int in_cycle=0;

int find_set(int a)
{
    if(a==u[a]) return a;
    else return u[a]=find_set(u[a]);
}

int merge_sets(int a,int b)
{
    a=find_set(a);
    b=find_set(b);
    if(a==b) return 0;
    u[b]=a;
    return 1;
}

void chmax(ll &a,ll b){a=max(a,b);}

void dfs(int a)
{
    cycle[cyclesz++]=a;
    ll one=0,two=0;
    for(int i=vidx[a];i<vsz&&v[i][0]==a;i++)
    {
        auto [_,to,c]=v[i];
        if(to==u[a]) continue;
        u[to]=a;
        dfs(to);
        ll len=c+down[to];
        if(len>one){two=one; one=len;}
        else if(len>two){two=len;}
        chmax(dp[a],dp[to]);
        chmax(down[a],len);
    }
    chmax(dp[a],one+two);
}

void go(int a,int p)
{
    for(int i=vidx[a];i<vsz&&v[i][0]==a;i++)
    {
        auto [_,to,c]=v[i];
        if(to==p||to==in_cycle) continue;
        go(to,a);
        chmax(down[a],c+down[to]);
    }
}

int ucost(int i)
{
    for(int j=vidx[cycle[i]];j<vsz&&v[j][0]==cycle[i];j++)
    {
        auto [_,to,c]=v[j];
        if(to==cycle[i+1]) return c;
    }
    return 0;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    for(int i=1;i<=n;i++) u[i]=i;
    for(int a=1;a<=n;a++)
    {
        int b,c;
        cin >> b >> c;
        if(merge_sets(a,b))
        {
            v[vsz++]={a,b,c};
            v[vsz++]={b,a,c};
        }
        else v[--badidx]={a,b,c};
    }
    sort(v,v+vsz);
    for(int i=vsz-1;i>=0;i--) vidx[v[i][0]]=i;
    ll res=0;
    memset(u,0,sizeof(u));
    for(int o=2*N-1;o>=badidx;o--)
    {
        auto [x,y,bad_cost]=v[o];
        dfs(x);
        ll now=dp[x];
        for(int i=0;i<cyclesz;i++) down[cycle[i]]=dp[cycle[i]]=0;
        cyclesz=0;
        int t=y;
        while(t!=0)
        {
            cycle[cyclesz++]=t;
            t=u[t];
        }
        for(int i=0;i<cyclesz;i++)
        {
            if(i+1<cyclesz) in_cycle=cycle[i+1];
            go(cycle[i],(i>0?cycle[i-1]:0));
        }
        ll path=0;
        for(int i=0;i<cyclesz;i++)
        {
            if(i>0) dp[cycle[i]]=dp[cycle[i-1]];
            chmax(dp[cycle[i]],path+down[cycle[i]]);
            if(i+1<cyclesz) path+=ucost(i);
        }
        path=0;
        ll opt=0;
        for(int i=cyclesz-1;i>=0;i--)
        {
            if(i+1<cyclesz) path+=ucost(i);
            chmax(opt,path+down[cycle[i]]);
            if(i>0) chmax(now,dp[cycle[i-1]]+bad_cost+opt);
        }
        res+=now;
        cyclesz=0;
    }
    cout << res << "\n";
    return 0;
}

• 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: 10 / 10