Submission #198239

#	Time	Username	Problem	Language	Result	Execution time	Memory
198239		mehrdad_sohrabi	Beads and wires (APIO14_beads)	C++14	100 / 100	275 ms	23448 KiB

beads

#include <bits/stdc++.h>
typedef int ll;
typedef long double ld;
#define pb push_back
#define pii pair < int, int >
#define F first
#define S second
//#define int long long int
#define sync ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)

#define endl '\n'
using namespace std;
const int N=2e5+100;
vector <pii> g[N];
ll vis[N];
ll ans=0;
ll dp[N][2];
void dfs(ll v,ll p,ll w){
    ll ma=-1e9;
    ll d=0;
    for (auto u : g[v]){
        if (u.F==p) continue;
        dfs(u.F,v,u.S);
        dp[v][1]+=dp[u.F][0];
        d+=dp[u.F][0];
        ma=max(ma,u.S+dp[u.F][1]-dp[u.F][0]);
    }
    if (p!=-1 && ma>-1e9){
        ll cnt=d+ma+w;
        dp[v][0]=max(dp[v][1],cnt);
    }
}
ll up[N][2];
ll dfs2(ll v,ll p){
    ll cnt=0,wp=0;
    for (auto u : g[v]){
        if (u.F==p){
            wp=u.S;
            continue;
        }
        cnt+=dp[u.F][0];
    }
    cnt+=up[v][0];
    for (auto u : g[v]){
        if (u.F==p) continue;
        up[u.F][1]=cnt-dp[u.F][0];
    }
    for (auto u : g[v]){
        if (u.F==p || v==1) continue;
        up[u.F][0]=max(up[u.F][0],u.S+wp+cnt-dp[u.F][0]-up[v][0]+up[v][1]);
    }
    ll mx=-1e9;
    for (auto u : g[v]){
        ll z=cnt;
        if (u.F==p) continue;
        /*
        for (auto q : g[v]){
            if (u.F==q.F || q.F==p) continue;
            ll t=z-dp[u.F][0]-dp[q.F][0]+dp[q.F][1]+u.S+q.S;
            up[u.F][0]=max(up[u.F][0],t);
        }
        */
        ll t=z+mx-dp[u.F][0]+u.S;
        up[u.F][0]=max(up[u.F][0],t);
        up[u.F][0]=max(up[u.F][0],up[u.F][1]);
        mx=max(mx,-dp[u.F][0]+dp[u.F][1]+u.S);
    }
    mx=-1e9;
    reverse(g[v].begin(),g[v].end());
    for (auto u : g[v]){
        ll z=cnt;
        if (u.F==p) continue;
        /*
        for (auto q : g[v]){
            if (u.F==q.F || q.F==p) continue;
            ll t=z-dp[u.F][0]-dp[q.F][0]+dp[q.F][1]+u.S+q.S;
            up[u.F][0]=max(up[u.F][0],t);
        }
        */
        ll t=z+mx-dp[u.F][0]+u.S;
        up[u.F][0]=max(up[u.F][0],t);
        up[u.F][0]=max(up[u.F][0],up[u.F][1]);
        mx=max(mx,-dp[u.F][0]+dp[u.F][1]+u.S);
    }
    for (auto u : g[v]){
        if (u.F!=p) dfs2(u.F,v);
    }
}
int32_t main(){
    sync;
    ll n;
    cin >> n;
    for (int i=0;i<n-1;i++){
        ll u,v,w;
        cin >> u >> v >> w;
        g[u].pb({v,w});
        g[v].pb({u,w});
    }
    for (int i=1;i<=n;i++){
        vector <pii> a;
        for (auto  q : g[i]){
           ll u=q.F;
            if (g[u].size()==1) a.pb({q.S,u});
        }
        sort(a.begin(),a.end());
        for (int j=1;j<a.size();j++){
            vis[a[j].S]=1;
        }
    }
    ll ma=0;
    ll cnt=0;
    dfs(1,-1,0);
    dfs2(1,1);
    for (int i=1;i<=n;i++){
        ma=max(ma,dp[i][1]+up[i][0]);
        //cout << i << " " << dp[i][1] << " " << up[i][0] << " " << ma << endl;
    }
    cout << ma << endl;
}
/*
10
4 10 2
1 2 21
1 3 13
6 7 1
7 9 5
2 4 3
2 5 8
1 6 55
6 8 34
*/
/*
6
1 2 20
2 3 20
3 4
10
3 5 10
3 6 10
*/

Compilation message (stderr)

beads.cpp: In function 'll dfs2(ll, ll)':
beads.cpp:88:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
beads.cpp: In function 'int32_t main()':
beads.cpp:106:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j=1;j<a.size();j++){
                      ~^~~~~~~~~
beads.cpp:111:8: warning: unused variable 'cnt' [-Wunused-variable]
     ll cnt=0;
        ^~~

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