Submission #39303

#	Time	Username	Problem	Language	Result	Execution time	Memory
39303		qoo2p5	Beads and wires (APIO14_beads)	C++14	100 / 100	399 ms	25580 KiB

beads

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int INF = (int) 1e9 + 1e6 + 123;
const ll LINF = (ll) 1e18 + 1e9 + 123;
const ld EPS = (ld) 1e-7;
const ll MOD = (ll) 1e9 + 7;

#define sz(x) (int) (x).size()
#define mp(x, y) make_pair(x, y)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define lb(s, t, x) (int) (lower_bound(s, t, x) - s)
#define ub(s, t, x) (int) (upper_bound(s, t, x) - s)
#define rep(i, f, t) for (int i = f; i < t; i++)
#define per(i, f, t) for (int i = f; i >= t; i--)

ll power(ll x, ll y, ll mod = MOD) {
    if (y == 0) {
        return 1;
    }
    if (y & 1) {
        return power(x, y - 1, mod) * x % mod;
    } else {
        ll tmp = power(x, y / 2, mod);
        return tmp * tmp % mod;
    }
}

template<typename A, typename B> bool mini(A &x, const B &y) {
    if (y < x) {
        x = y;
        return true;
    }
    return false;
}

template<typename A, typename B> bool maxi(A &x, const B &y) {
    if (y > x) {
        x = y;
        return true;
    }
    return false;
}

void add(ll &x, ll y) {
	x += y;
	if (x >= MOD) x -= MOD;
	if (x < 0) x += MOD;
}

ll mult(ll x, ll y) {
	return x * y % MOD;
}

void run();

#define TASK ""

int main() {
#ifdef LOCAL
    if (strlen(TASK) > 0) {
        cerr << "Reminder: you are using file i/o, filename: " TASK "!" << endl << endl;
    }
#endif
#ifndef LOCAL
    if (strlen(TASK)) {
        freopen(TASK ".in", "r", stdin);
        freopen(TASK ".out", "w", stdout);
    }
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
#endif
    cout << fixed << setprecision(12);
    run();
    return 0;
}

// == SOLUTION == //

const int N = (int) 2e5 + 123;

int n;
vector<pair<int, int>> g[N];
int take[N], ntake[N];
ll ans;

void dfs1(int v, int f = -1, int up_w = 0) {
	ntake[v] = 0;
	take[v] = 0;
	
	rep(i, 0, sz(g[v])) {
		int u = g[v][i].first;
		if (u == f) {
			continue;
		}
		dfs1(u, v, g[v][i].second);
		ntake[v] += take[u];
	}
	
	if (f != -1) {
		for (auto &it : g[v]) {
			int u = it.first;
			if (u == f) {
				continue;
			}
			maxi(take[v], ntake[v] - take[u] + ntake[u] + it.second + up_w);
		}
	}
	
	maxi(take[v], ntake[v]);
}

void dfs2(int v, int f = -1, int up = 0, int prv_up = 0, int up_w = 0) {
	multiset<int> q;
	for (auto &it : g[v]) {
		int u = it.first;
		if (u == f) {
			continue;
		}
		q.insert(-take[u] + ntake[u] + it.second);
	}
	for (auto &it : g[v]) {
		int u = it.first;
		if (u == f) {
			continue;
		}
		
		q.erase(q.find(-take[u] + ntake[u] + it.second));
		
		int nup = up + ntake[v] - take[u];
		if (f != -1) {
			maxi(nup, ntake[v] - take[u] + prv_up + ntake[f] - take[v] + it.second + up_w);
		}
		if (sz(q)) maxi(nup, ntake[v] - take[u] + up + *q.rbegin() + it.second);
		dfs2(u, v, nup, up, it.second);
		
		q.insert(-take[u] + ntake[u] + it.second);
	}
	
	maxi(ans, ntake[v] + up);
}

void run() {
	cin >> n;
	rep(i, 1, n) {
		int u, v, c;
		cin >> u >> v >> c;
		g[u].pb({v, c});
		g[v].pb({u, c});
	}
	
	dfs1(1);
	ans = ntake[1];
	dfs2(1);
	
	cout << ans << "\n";
}

Compilation message (stderr)

beads.cpp: In function 'int main()':
beads.cpp:72:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
         freopen(TASK ".in", "r", stdin);
         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:73:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
         freopen(TASK ".out", "w", stdout);
         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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