Submission #1041894

#	Time	Username	Problem	Language	Result	Execution time	Memory
1041894		MMihalev	Beads and wires (APIO14_beads)	C++14	100 / 100	70 ms	28100 KiB

beads

#include<iostream>
#include<algorithm>
#include<iomanip>
#include<cmath>
#include<cstring>
#include<vector>
#include<queue>
#include<stack>
#include<tuple>
#include<set>
#include<map>
#include<random>
#include<chrono>
using namespace std;
const int MAX_N=2e5+1;
const int INF=2e9+1e8;
int dpdown[MAX_N][2];
int dpup[MAX_N][2];
int best[MAX_N];
int best2[MAX_N];
int sum[MAX_N];
int n;
vector<pair<int,int>>g[MAX_N];
void dfsdown(int u,int par)
{
    vector<int>ch;
    for(auto [v,edge]:g[u])
    {
        if(v==par)continue;
        dfsdown(v,u);

        sum[u]+=max(edge+dpdown[v][1],dpdown[v][0]);
        ch.push_back(-max(edge+dpdown[v][1],dpdown[v][0])+edge+dpdown[v][0]);
    }

    sort(ch.rbegin(),ch.rend());

    if(ch.size())
    {
        dpdown[u][1]=sum[u]+ch[0];
        best[u]=ch[0];
    }
    else dpdown[u][1]=-INF;

    if(ch.size()>1)best2[u]=ch[1];

    dpdown[u][0]=sum[u];
}
void dfsup(int u,int par)
{
    for(auto [v,edge]:g[u])
    {
        if(v==par)continue;

        int cur1=max(edge+dpdown[v][1],dpdown[v][0]);
        int cur2=-cur1+edge+dpdown[v][0];


        dpup[v][1]=sum[u]-cur1+edge+dpup[u][0];

        dpup[v][0]=max((g[u].size()-(par!=0)>=2 ? sum[u]+(cur2==best[u] ? best2[u] : best[u])-cur1+dpup[u][0]+edge : 0),//put blue in subtree
                       sum[u]-cur1+dpup[u][1]+edge);                               //put blue up
        dpup[v][0]=max(dpup[v][0],sum[u]-cur1+dpup[u][0]);//put red


        dfsup(v,u);
    }
}
signed main ()
{
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout.tie(NULL);
    cin>>n;
    for(int i=1;i<n;i++)
    {
        int u,v,c;
        cin>>u>>v>>c;
        g[u].push_back({v,c});
        g[v].push_back({u,c});
    }

    dfsdown(1,0);
    dpup[1][1]=-INF;
    dfsup(1,0);

    int ans=0;
    for(int i=1;i<=n;i++)
    {
        ans=max(ans,dpdown[i][0]+dpup[i][0]);
    }
    cout<<ans<<"\n";
    return 0;
}

Compilation message (stderr)

beads.cpp: In function 'void dfsdown(int, int)':
beads.cpp:27:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   27 |     for(auto [v,edge]:g[u])
      |              ^
beads.cpp: In function 'void dfsup(int, int)':
beads.cpp:51:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   51 |     for(auto [v,edge]:g[u])
      |              ^

• Subtask 1: 13 / 13
• Subtask 2: 15 / 15
• Subtask 3: 29 / 29
• Subtask 4: 43 / 43