Submission #1166044

#	Time	Username	Problem	Language	Result	Execution time	Memory
1166044		Sang	Beads and wires (APIO14_beads)	C++20	100 / 100	77 ms	28340 KiB

beads

#include<bits/stdc++.h>
using namespace std;

#define int long long
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i++)
#define FORD(i, a, b) for (int i = (a), _b = (b); i >= _b; i--)
#define fi first
#define se second
#define pb push_back
#define ALL(a) (a).begin(), (a).end()
#define task "kbsiudthw"

typedef vector<int> vi;
typedef pair<int, int> ii;
typedef pair<int, ii> pii;

const int N = 2e5 + 5;
const int INF = 1e18;
const int MOD = 1e9 + 2277;

int n, dp[N][2][2], e[N];

vector<ii> G[N];

void dfs(int u, int par){
    int f = -INF, s = -INF, f2 = -INF, s2 = -INF, best = -INF;
    int id1 = -1, id2 = -1, id3 = -1, id4 = -1, tot = 0;

    for (ii &v : G[u]){
        if (v.fi == par) continue;
        e[v.fi] = v.se;
        dfs(v.fi, u);
        int nor = max(dp[v.fi][0][0], dp[v.fi][1][0]);
        tot += nor;
        best = max(best, max(dp[v.fi][0][1], dp[v.fi][1][1]) - nor);
        int d = dp[v.fi][0][1] + v.se - nor;
        if (d > f){
            s = f;
            id2 = id1;

            f = d;
            id1 = v.fi;
        } else if (d > s){
            s = d;
            id2 = v.fi;
        }

        int d2 = dp[v.fi][0][0] + v.se - nor;

        if (d2 > f2){
            s2 = f2;
            id4 = id3;

            f2 = d2;
            id3 = v.fi;
        } else if (d2 > s2){
            s2 = d2;
            id4 = v.fi;
        }
    }
    dp[u][0][0] = tot;
    dp[u][0][1] = max(tot + max(0ll, best), tot + f2 + s2);
    if (id1 != id3){
        dp[u][0][1] = max(dp[u][0][1], tot + f + f2);
    } else {
        dp[u][0][1] = max(dp[u][0][1], tot + max(f + s2, f2 + s));
    }
    dp[u][1][0] = tot + e[u] + f2;
    dp[u][1][1] = tot + e[u] + f;
}

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    if (fopen(task".inp", "r")){
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    cin >> n;
    FOR (i, 2, n){
        int u, v, w; cin >> u >> v >> w;
        G[u].pb({v, w});
        G[v].pb({u, w});
    }
    dfs(1, 0);
    cout << max(dp[1][0][0], dp[1][0][1]);

    return 0;
}

Compilation message (stderr)

beads.cpp: In function 'int main()':
beads.cpp:76:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   76 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:77:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   77 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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