Submission #672774

#	Time	Username	Problem	Language	Result	Execution time	Memory
672774		Hanksburger	Beads and wires (APIO14_beads)	C++17	100 / 100	304 ms	79100 KiB

beads

#include <bits/stdc++.h>
#define ll long long
using namespace std;
vector<pair<ll, ll> > adj[200005], child[200005];
ll f[200005][2], mx[200005], mx2[200005], ans;
vector<ll> g[200005][2], h[200005][2];
pair<ll, ll> par[200005];
void dfs0(ll u)
{
    for (ll i=0; i<adj[u].size(); i++)
    {
        int v=adj[u][i].first, w=adj[u][i].second;
        if (v==par[u].first)
            continue;
        par[v]={u, child[u].size()};
        child[u].push_back({v, w});
        dfs0(v);
    }
}
void dfs1(ll u)
{
//    cout << "dfs " << u << '\n';
    mx[u]=mx2[u]=-1e18;
    for (ll i=0; i<child[u].size(); i++)
    {
        ll v=child[u][i].first, w=child[u][i].second;
        dfs1(v);
        f[u][0]+=max(f[v][0], f[v][1]+w);
        ll z=f[v][0]+w-max(f[v][0], f[v][1]+w);
        if (mx[u]<=z)
        {
            mx2[u]=mx[u];
            mx[u]=z;
        }
        else if (mx2[u]<z)
            mx2[u]=z;
    }
    f[u][1]=f[u][0]+mx[u];
//    cout << "f[" << u << "][0] " << f[u][0] << '\n';
//    cout << "f[" << u << "][1] " << f[u][1] << '\n';
    for (ll i=0; i<child[u].size(); i++)
    {
        ll v=child[u][i].first, w=child[u][i].second;
        g[u][0].push_back(f[u][0]-max(f[v][0], f[v][1]+w));
        if (mx[u]==f[v][0]+w-max(f[v][0], f[v][1]+w))
            g[u][1].push_back(g[u][0][i]+mx2[u]);
        else
            g[u][1].push_back(g[u][0][i]+mx[u]);
    }
}
void dfs2(ll u)
{
//    cout << "dfs2 " << u << '\n';
    ll p=par[u].first, j=par[u].second;
    ll x=(u==1?0:child[p][j].second);
    for (ll i=0; i<child[u].size(); i++)
    {
        ll v=child[u][i].first, w=child[u][i].second;
        if (u==1)
        {
            h[u][0].push_back(g[u][0][i]);
            h[u][1].push_back(g[u][1][i]);
        }
        else
        {
            h[u][0].push_back(g[u][0][i]+max(h[p][0][j], h[p][1][j]+x));
            h[u][1].push_back(max(g[u][0][i]+h[p][0][j]+x, g[u][1][i]+max(h[p][0][j], h[p][1][j]+x)));
        }
        ans=max(ans, f[v][0]+max(h[u][0][i], h[u][1][i]+w));
        dfs2(v);
    }
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    ll n;
    cin >> n;
    for (ll i=1; i<n; i++)
    {
        ll u, v, w;
        cin >> u >> v >> w;
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }
    dfs0(1);
    dfs1(1);
    dfs2(1);
    cout << max(ans, f[1][0]);
}

Compilation message (stderr)

beads.cpp: In function 'void dfs0(long long int)':
beads.cpp:10:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |     for (ll i=0; i<adj[u].size(); i++)
      |                  ~^~~~~~~~~~~~~~
beads.cpp: In function 'void dfs1(long long int)':
beads.cpp:24:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |     for (ll i=0; i<child[u].size(); i++)
      |                  ~^~~~~~~~~~~~~~~~
beads.cpp:41:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   41 |     for (ll i=0; i<child[u].size(); i++)
      |                  ~^~~~~~~~~~~~~~~~
beads.cpp: In function 'void dfs2(long long int)':
beads.cpp:56:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   56 |     for (ll i=0; i<child[u].size(); i++)
      |                  ~^~~~~~~~~~~~~~~~

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