Submission #670104

#	Time	Username	Problem	Language	Result	Execution time	Memory
670104		radal	Beads and wires (APIO14_beads)	C++17	0 / 100	3 ms	4948 KiB

beads

#include <bits/stdc++.h>
#pragma GCC target("sse,sse2,avx2")
#pragma GCC optimize("unroll-loops,O2")
#define rep(i,l,r) for (int i = l; i < r; i++)
#define repr(i,r,l) for (int i = r; i >= l; i--)
#define X first
#define Y second
#define all(x) (x).begin() , (x).end()
#define pb push_back
#define endl '\n'
#define debug(x) cerr << #x << " : " << x << endl;
using namespace std;
typedef long long ll;
typedef pair<int,int> pll;
constexpr int N = 2e5+10,mod = 1e9+7,maxm = 210;
constexpr ll inf = 1e9+10;
inline int mkay(int a,int b){
    if (a+b >= mod) return a+b-mod;
   // if (a+b < 0) return a+b+mod;
    return a+b;
}

inline int poww(int a,int k){
    if (k < 0) return 0;
    int z = 1;
    while (k){
        if (k&1) z = 1ll*z*a%mod;
        a = 1ll*a*a%mod;
        k >>= 1;
    } 
    return z; 
}

vector<pll> adj[N];
int dp[N][2][2];

void dfs(int v,int p,int pw){
	if ((int) adj[v].size() == 1){
		dp[v][1][0] = dp[v][1][1] = dp[v][0][1] = -2*inf;
		dp[v][0][0] = 0;
		return;
	}
	vector<int> ve;
	int s = 0;
	for (auto [u,w] : adj[v]){
		if (u == p) continue;
		dfs(u,v,w);
		int val = max({dp[u][0][0],dp[u][0][1],dp[u][1][0],dp[u][1][1]});
		s += val;
		ve.pb(max(dp[u][1][0],dp[u][0][0])-val+w);

	}
	sort(all(ve));
	int sz = ve.size();
	dp[v][0][0] = s;
	dp[v][0][1] = -2*inf;
	dp[v][1][1] = s+ve.back()+pw;
	if (sz > 1) dp[v][1][0] = s+ve[sz-1]+ve[sz-2];
	else dp[v][1][0] = -2*inf;
}

int main(){
	ios :: sync_with_stdio(0); cin.tie(0); 
	int n;
	cin >> n;
	rep(i,1,n){
		int u,v,w;
		cin >> u >> v >> w;
		adj[u].pb({v,w});
		adj[v].pb({u,w});
	}
	if (n <= 2){
		cout << 0 << endl;
		return 0;
	}
	int r = -1;
	rep(i,1,n+1) if ((int) adj[i].size() > 1){
	   	r = i;
		break;
	}
	dfs(r,0,-2*inf);
	cout << max(dp[r][1][0],dp[r][0][0]);
}

• Subtask 1: 0 / 13
• Subtask 2: 0 / 15
• Subtask 3: 0 / 29
• Subtask 4: 0 / 43