Submission #563259

#	Time	Username	Problem	Language	Result	Execution time	Memory
563259		tranxuanbach	Beads and wires (APIO14_beads)	C++17	100 / 100	261 ms	32892 KiB

beads

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

#define endl '\n'
#define fi first
#define se second
#define For(i, l, r) for (auto i = (l); i < (r); i++)
#define ForE(i, l, r) for (auto i = (l); i <= (r); i++)
#define FordE(i, l, r) for (auto i = (l); i >= (r); i--)
#define Fora(v, a) for (auto v: (a))
#define bend(a) (a).begin(), (a).end()
#define isz(a) ((signed)(a).size())

using ll = long long;
using ld = long double;
using pii = pair <int, int>;
using vi = vector <int>;
using vpii = vector <pii>;
using vvi = vector <vi>;

const int N = 2e5 + 5;
const ll infll = (ll)1e18 + 7;

int n;
vpii adj[N];

int wpar[N];

void dfs(int u, int p){
    Fora(&edge, adj[u]){
        int v, w; tie(v, w) = edge;
        if (v == p){
            continue;
        }
        wpar[v] = w;
        dfs(v, u);
    }
}

ll dp[N][2];

void dfs_dp(int u, int p){
    ll sum = 0, mx = -infll;
    Fora(&edge, adj[u]){
        int v, w; tie(v, w) = edge;
        if (v == p){
            continue;
        }
        dfs_dp(v, u);
        sum += dp[v][0];
        mx = max(mx, dp[v][1] - dp[v][0]);
    }
    dp[u][0] = max(sum, sum + mx + wpar[u]);
    dp[u][1] = sum + wpar[u];
}

ll ans = -infll;

void dfs_reroot(int u, int p){
    ans = max(ans, dp[u][0]);

    vector <ll> prefmx(isz(adj[u])), suffmx(isz(adj[u]));

    For(i, 0, isz(adj[u])){
        int v, w; tie(v, w) = adj[u][i];
        prefmx[i] = max(i > 0 ? prefmx[i - 1] : -infll, dp[v][1] - dp[v][0]);
    }
    FordE(i, isz(adj[u]) - 1, 0){
        int v, w; tie(v, w) = adj[u][i];
        suffmx[i] = max(i < isz(adj[u]) - 1 ? suffmx[i + 1] : -infll, dp[v][1] - dp[v][0]);
    }

    int owparu = wpar[u]; ll odpu0 = dp[u][0], odpu1 = dp[u][1], osumu = dp[u][1] - wpar[u];
    For(i, 0, isz(adj[u])){
        int v, w; tie(v, w) = adj[u][i];
        if (v == p){
            continue;
        }
        int owparv = wpar[v]; ll odpv0 = dp[v][0], odpv1 = dp[v][1], osumv = dp[v][1] - wpar[v];
        ll mx = -infll;
        Fora(&edge, adj[v]){
            int tv, tw; tie(tv, tw) = edge;
            if (tv == u){
                continue;
            }
            mx = max(mx, dp[tv][1] - dp[tv][0]);
        }

        wpar[u] = w;
        dp[u][0] = max(osumu - dp[v][0], osumu - dp[v][0] + max(i > 0 ? prefmx[i - 1] : -infll, i < isz(adj[u]) - 1 ? suffmx[i + 1] : -infll) + wpar[u]);
        dp[u][1] = osumu - dp[v][0] + wpar[u];
        wpar[v] = -1e9;
        dp[v][0] = max(osumv + dp[u][0], osumv + dp[u][0] + max(mx, dp[u][1] - dp[u][0]) + wpar[v]);
        dp[v][1] = osumv + dp[u][0] + wpar[v];

        dfs_reroot(v, u);

        wpar[v] = owparv; dp[v][0] = odpv0; dp[v][1] = odpv1;
    }
    wpar[u] = owparu; dp[u][0] = odpu0; dp[u][1] = odpu1;
}

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    // freopen("KEK.inp", "r", stdin);
    // freopen("KEK.out", "w", stdout);
    cin >> n;
    For(i, 1, n){
        int u, v, w; cin >> u >> v >> w;
        adj[u].emplace_back(v, w);
        adj[v].emplace_back(u, w);
    }

    wpar[1] = -1e9;
    dfs(1, 0);
    dfs_dp(1, 0);
    dfs_reroot(1, 0);

    cout << ans << endl;
}

/*
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OUTPUT:                                           |
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*/

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