Submission #972392

#	Time	Username	Problem	Language	Result	Execution time	Memory
972392		pcc	Beads and wires (APIO14_beads)	C++17	100 / 100	217 ms	34752 KiB

beads

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

#define ll long long
#define pll pair<ll,ll>
#define pii pair<int,int>
#define fs first
#define sc second
#define tlll tuple<ll,ll,ll>

const int mxn = 2e5+10;
vector<pii> tree[mxn];
int dp[mxn][2];
int N;
int ans = 0;
vector<pii> v[mxn];

void dfs(int now,int par){
	dp[now][0] = 0;
	dp[now][1] = -1e9;
	for(auto [nxt,w]:tree[now]){
		if(nxt == par)continue;
		dfs(nxt,now);
		dp[now][0] += max(dp[nxt][0],dp[nxt][1]+w);
		v[now].push_back(pii(dp[nxt][0]+w-max(dp[nxt][0],dp[nxt][1]+w),nxt));
	}
	sort(v[now].rbegin(),v[now].rend());
	if(!v[now].empty())dp[now][1] = dp[now][0]+v[now][0].fs;
	return;
}

void dfs2(int now,int par){
	ans = max(ans,dp[now][0]);
	sort(v[now].rbegin(),v[now].rend());
	for(auto [nxt,w]:tree[now]){
		if(nxt == par)continue;
		int dp0 = dp[now][0]-max(dp[nxt][0],dp[nxt][1]+w);
		int dp1 = -1e9;
		if(v[now][0].sc != nxt)dp1 = dp0+v[now][0].fs;
		else if(v[now].size()>1)dp1 = dp0+v[now][1].fs;
		dp[nxt][0] += max(dp0,dp1+w);
		v[nxt].push_back(pii(dp0+w-max(dp0,dp1+w),now));
		dfs2(nxt,now);
	}
	return;
}

int main(){
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin>>N;
	for(int i = 1;i<N;i++){
		int a,b,c;
		cin>>a>>b>>c;
		tree[a].push_back(pii(b,c));
		tree[b].push_back(pii(a,c));
	}
	dfs(1,1);
	dfs2(1,1);
	cout<<ans<<'\n';
	return 0;
}

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