Submission #312762

#	Time	Username	Problem	Language	Result	Execution time	Memory
312762		hohohaha	Beads and wires (APIO14_beads)	C++14	100 / 100	552 ms	32868 KiB

beads

#include<bits/stdc++.h>

using namespace std;

#define int long long

#define ii pair<int, int>
#define iii pair<ii, int>

#define mp make_pair
#define eb emplace_back

#define vi vector<int>
#define vii vector<ii>
#define viii vector<iii>

#define fi first
#define se second
#define xx fi.fi
#define yy fi.se
#define zz se
int n, ans, mxw[200005][2], dp[200005][2], pw[200005], p[200005];
vii G[200005];
void dfs(int u)
{
	int mxr = LLONG_MIN/100LL;
	for(ii e: G[u])
	{
		int v = e.fi, w = e.se;
		if(v!=p[u])
		{
			p[v] = u;
			pw[v] = w;
			dfs(v);
			dp[u][0]+=dp[v][1];
			int replace = dp[v][0] - dp[v][1] + w;
			mxr = max(mxr, replace);
			int temp = mxw[u][0], mx0 = mxw[u][0], mx1 = mxw[u][1];
			if(!mx0 or replace>dp[mx0][0] - dp[mx0][1] + pw[mx0])
			{
				mxw[u][1] = mxw[u][0];
				mxw[u][0] = v;
			}
			else if(!mx1 or replace> dp[mx1][0] - dp[mx1][1] + pw[mx1])
			{
				mxw[u][1] = v;
			}
		}
	}
	dp[u][1] = max(dp[u][0], (u==1? LLONG_MIN/100LL: pw[u] + mxr + dp[u][0])); //toi quen th u = 1 ditme
//	cout<<u<<" "<<dp[u][0]<<" "<<dp[u][1]<<endl;
}
void euler(int u)
{
	ans = max(ans, dp[u][0]);
	for(ii e: G[u])
	{
		int v = e.fi, w = e.se;
		if(v!=p[u])
		{
			// reroot
			int tu0 = dp[u][0], tu1 = dp[u][1], tv0 = dp[v][0], tv1 = dp[v][1];
			int mxid = mxw[u][0]==v? mxw[u][1]: mxw[u][0];
			int mx = max((!mxid? LLONG_MIN/100ll: dp[mxid][0] - dp[mxid][1] + pw[mxid]), (!p[u]? LLONG_MIN/100LL: dp[p[u]][0] - dp[p[u]][1] + pw[u])); // toi quen truong hop mxid = 0 ditme
			dp[u][0] = dp[u][0] - dp[v][1];
			dp[u][1] = max(dp[u][0], dp[u][0] + mx + w);
			dp[v][0] = dp[v][1] = dp[v][0]+dp[u][1]; 
//			cout<<mx<<endl;
//			cout<<u<<" "<<v<<" "<<dp[u][0]<<" "<<dp[u][1]<<" "<<dp[v][1]<<endl;
			euler(v);
			//rollback
			dp[u][0] = tu0, dp[u][1] = tu1, dp[v][0] = tv0, dp[v][1] = tv1;
		}
	}
}
signed main()
{
// 	freopen(".inp", "r", stdin);
// 	freopen(".out", "w", stdout);
// 	ios_base::sync_with_stdio(false);
//    cin.tie(NULL);
//    cout.tie(NULL);
    cin>>n;
    for(int i=1; i<=n-1; i++)
    {
    	int u, v, w;
    	cin>>u>>v>>w;
    	G[u].eb(v, w);
    	G[v].eb(u, w);
	}
	dfs(1);
	euler(1);
	cout<<ans;
}

Compilation message (stderr)

beads.cpp: In function 'void dfs(long long int)':
beads.cpp:38:8: warning: unused variable 'temp' [-Wunused-variable]
   38 |    int temp = mxw[u][0], mx0 = mxw[u][0], mx1 = mxw[u][1];
      |        ^~~~

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