Submission #198268

#	Time	Username	Problem	Language	Result	Execution time	Memory
198268		alishahali1382	Beads and wires (APIO14_beads)	C++14	100 / 100	286 ms	36476 KiB

beads

#include <bits/stdc++.h>
#pragma GCC optimize ("O2")
#pragma GCC optimize ("unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")

#define int long long

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;

const ld eps=1e-7;
const int inf=2000000010;
const ll INF=10000000000000010LL;
const int mod = 1000000007;
const int MAXN = 200010, LOG=20;

int n, m, k, u, v, x, y, t, a, b, ans;
int dp[MAXN][2];
int sum[MAXN];
//int dp2[MAXN][2];
pii mx[MAXN][2];
vector<pii> G[MAXN];

void dfs1(int node, int par){
	dp[node][0]=0;
	dp[node][1]=-inf;
	for (pii p:G[node]) if (p.first!=par) dfs1(p.first, node);
	
	sum[node]=0;
	for (pii p:G[node]) if (p.first!=par) sum[node]+=max(dp[p.first][0], dp[p.first][1]+p.second);
	dp[node][0]=sum[node];
	
	mx[node][0]=mx[node][1]={-inf, 0};
	for (pii p:G[node]) if (p.first!=par){
		pii tmp={min(p.second, dp[p.first][0]-dp[p.first][1]), p.first};
		if (tmp>mx[node][1]) mx[node][1]=tmp;
		if (mx[node][1]>mx[node][0]) swap(mx[node][0], mx[node][1]);
	}
	dp[node][1]=sum[node]+mx[node][0].first;
	
	//dp[node][0]=sum;
	
}

void dfs2(int node, int par){
	ans=max(ans, dp[node][0]);
	int parw=0;
	for (pii p:G[node]) if (p.first==par) parw=p.second;
	
	for (pii p:G[node]) if (p.first!=par){
		int v=p.first, w=p.second;
		int nd0=dp[node][0], nd1=dp[node][1], ns=sum[node];
		int vd0=dp[v][0], vd1=dp[v][1], vs=sum[v];
		
		sum[node]-=max(dp[v][0], dp[v][1]+w);
		dp[node][0]=sum[node];
		dp[node][1]=-inf;
		
		dp[node][1]=sum[node]+mx[node][0].first;
		if (v==mx[node][0].second) dp[node][1]=sum[node]+mx[node][1].first;
		if (node!=1) dp[node][1]=max(dp[node][1], sum[node]+min(parw, dp[par][0]-dp[par][1]));
		
		//for (pii pp:G[node]) if (/*pp.first!=par && */pp.first!=v) dp[node][1]=max(dp[node][1], sum[node]+min(pp.second, dp[pp.first][0]-dp[pp.first][1]));
		
		sum[v]+=max(dp[node][0], dp[node][1]+w);
		dp[v][0]=sum[v];
		dp[v][1]=max(sum[v]+mx[v][0].first, sum[v]+min(w, dp[node][0]-dp[node][1]));
		
		dfs2(v, node);
		
		dp[node][0]=nd0;
		dp[node][1]=nd1;
		sum[node]=ns;
		dp[v][0]=vd0;
		dp[v][1]=vd1;
		sum[v]=vs;
	}
}

int32_t main(){
	ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	cin>>n;
	//assert(n<=10000);
	for (int i=1; i<n; i++){
		cin>>u>>v>>x;
		G[u].pb({v, x});
		G[v].pb({u, x});
	}
	
	/*
	for (int i=1; i<=n; i++){
		for (int j=1; j<=n; j++) dp[j][0]=0, dp[j][1]=-inf, sum[j]=0;
		dfs1(i, i);
		ans=max(ans, dp[i][0]);
		//debug2(i, dp[i][0])
	}*/
	
	dfs1(1, 1);
	dfs2(1, 1);
	
	cout<<ans<<'\n';
	
	return 0;
}
/*
5
1 2 10
1 3 40
1 4 15
1 5 20


10
4 10 2
1 2 21
1 3 13
6 7 1
7 9 5
2 4 3
2 5 8
1 6 55
6 8 34

*/

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