Submission #386433

#	Time	Username	Problem	Language	Result	Execution time	Memory
386433		Drew_	Beads and wires (APIO14_beads)	C++14	0 / 100	4 ms	5100 KiB

beads

#include <iostream>
#include <vector>
#include <algorithm>
#include <assert.h>
using namespace std;

#define int long long

#define pb push_back
#define ii pair<int, int>
#define f1 first
#define s2 second

const int MAX = 2e5 + 7;
const int inf = 1e9 + 7;

//dp[x][0]: do not use node x as center
//dp[x][1]: used the edge to the parent of node x
//dp[x][2]: used two edges to the child of node x (all graph)
//dp[x][3]: used two edges to the child of node x, and used the edge to the parent of node x

int dp[MAX][4];
vector<ii> adj[MAX];

int getLeaf(int node, int par)
{
	for (ii to : adj[node])
		if (to.f1 != par)
			return getLeaf(to.f1, node);
	return node;
}

void dfs(int node, int par, int par_val)
{
	vector<int> v[4];
	vector<int> edge;

	for (ii to : adj[node])
	{
		if (to.f1 != par)
		{
			dfs(to.f1, node, to.s2);

			for (int i = 0; i < 4; ++i)
				v[i].pb(dp[to.f1][i]);
			edge.pb(to.s2);
		}
	}

	if (v[0].empty())
		return;

	//not using node as center
	{
		for (int i = 0; i < v[0].size(); ++i)
			dp[node][0] += max(v[0][i], v[1][i]);
	}

	//using the edge to the parent
	{
		int ctr = 0;
		int mx = -inf;
		for (int i = 0; i < v[0].size(); ++i)
		{
			ctr += max(v[0][i], v[1][i]);

			if (v[0][i] <= v[1][i])
				mx = max(mx, edge[i] + v[0][i] - v[1][i]);
		}

		if (mx != -inf)
			dp[node][1] = ctr + mx + par_val;
	}

	//using a split
	{
		int ctr = 0;
		vector<int> val;
		for (int i = 0; i < v[0].size(); ++i)
		{
			dp[node][2] += max(max(v[0][i], v[1][i]), max(v[2][i], v[3][i]));
			
			ctr += max(v[0][i], v[1][i]);
			if (v[0][i] <= v[1][i])
				val.pb(edge[i] + v[0][i] - v[1][i]);
		}
		sort(val.begin(), val.end(), greater<int>());

		if (val.size() >= 2)
			dp[node][2] = max(dp[node][2], ctr + val[0] + val[1]);
	}

	//there has been a split, now uses the edge to the parent
	{
		int ctr = 0;
		int mx = -inf;
		for (int i = 0; i < v[0].size(); ++i)
		{
			ctr += max(v[2][i], v[3][i]);

			if (v[2][i] <= v[3][i])
				mx = max(mx, edge[i] + v[2][i] - v[3][i]);
		}

		if (mx != -inf)
			dp[node][3] = ctr + mx + par_val;
	}

	//cerr << node << "==> ";
	//for (int i = 0; i < 4; ++i)
	//	cerr << dp[node][i] << (i == 3 ? '\n' : ' ');
}

int32_t main()
{
	ios :: sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);

	int n;
	cin >> n;

	for (int i = 0; i < n-1; ++i)
	{
		int u, v, w;
		cin >> u >> v >> w;

		adj[u].pb({v, w});
		adj[v].pb({u, w});
	}

	int ROOT = getLeaf(1, -1);

	dfs(ROOT, -1, -1);
	
	cout << max(dp[ROOT][0], dp[ROOT][2]) << '\n';
	return 0;
}

Compilation message (stderr)

beads.cpp: In function 'void dfs(long long int, long long int, long long int)':
beads.cpp:55:21: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   55 |   for (int i = 0; i < v[0].size(); ++i)
      |                   ~~^~~~~~~~~~~~~
beads.cpp:63:21: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   63 |   for (int i = 0; i < v[0].size(); ++i)
      |                   ~~^~~~~~~~~~~~~
beads.cpp:79:21: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   79 |   for (int i = 0; i < v[0].size(); ++i)
      |                   ~~^~~~~~~~~~~~~
beads.cpp:97:21: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   97 |   for (int i = 0; i < v[0].size(); ++i)
      |                   ~~^~~~~~~~~~~~~

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