Submission #555897

#	Time	Username	Problem	Language	Result	Execution time	Memory
555897		blue	Pipes (BOI13_pipes)	C++17	74.07 / 100	66 ms	11648 KiB

pipes

#include <iostream>
#include <vector>
#include <queue>
#include <cassert>
using namespace std;

using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
using vpii = vector<pii>;
using vll = vector<ll>;
#define sz(x) int(x.size())

const int mx = 100'000;

int N, M;
vpii edge[1+mx];
vll c(1+mx);


vll x(1+mx);

void dfs(int u, int p)
{
	for(pii vp : edge[u])
	{
		int v = vp.first;
		int e = vp.second;

		if(v == p) continue;
		dfs(v, u);

		x[e] = 2*c[v];

		c[u] -= c[v];
		c[v] = 0;
	}
}

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	int N, M;
	cin >> N >> M;

	if(M > N)
	{
		cout << "0\n";
		return 0;
	}

	for(int i = 1; i <= N; i++) cin >> c[i];

	for(int j = 1; j <= M; j++)
	{
		int u, v;
		cin >> u >> v;
		edge[u].push_back({v, j});
		edge[v].push_back({u, j});
	}

	if(M == N-1)
	{
		dfs(1, 0);
	}
	else
	{
		queue<int> tbv;
		vi visit(1+N, 0);

		vi deg(1+N);
		for(int i = 1; i <= N; i++)
		{
			deg[i] = sz(edge[i]);
			if(deg[i] == 1)
			{
				tbv.push(i);
				visit[i] = 1;
			}
		}

		// cerr << "A\n";


		while(!tbv.empty())
		{
			int u = tbv.front();
			tbv.pop();

			for(auto vp : edge[u])
			{
				int v = vp.first;
				int e = vp.second;

				if(visit[v]) continue;

				deg[v]--;

				x[e] = 2*c[v];
				c[v] -= c[u];
				c[u] = 0;

				if(deg[v] == 1)
				{
					tbv.push(v);
					visit[v] = 1;
				}
			}
		}

		// cerr << "B\n";

		int U = 1;
		while(visit[U])
			U++;

		int viscount = 0;
		for(int u = 1; u <= N; u++)
			viscount += visit[u];

		vi edgevis(1+N, 0);

		// cerr << "C\n";


		vi nodes, edges;
		for(int z = 1; z <= N - viscount; z++)
		{
			for(auto vp : edge[U])
			{
				int v = vp.first;
				int e = vp.second;

				if(visit[v]) continue;
				if(edgevis[e]) continue;

				edgevis[e] = 1;


				nodes.push_back(U);
				edges.push_back(e);

				U = v;

				break;
			}
		}
		// cerr << "D\n";

		int Z = N - viscount;

		// cerr << "Z = " << Z << '\n';

		// for(int z = 0; z < Z; z++) cerr << nodes[z] << ' ' << edges[z] << '\n';

		if(Z % 2 == 0)
		{
			cout << "0\n";
			return 0;
		}

		vll a(Z), b(Z);
		a[0] = 1;
		b[0] = 0;



		for(int i = 1; i < Z; i++)
		{
			// if(!(1 <= nodes[i] && nodes[i] <= N)) while(1);
			a[i] = -a[i-1];
			b[i] = c[nodes[i]] - b[i-1]; 
		}

		// return 0;

		//(a.back() + a[0]) * x  +  (b.back() + b[0]) == c[nodes[0]]
		//x = (c[nodes[0]] - (b.back() + b[0])) / (a.back() + a[0])

		// if(a.back() + a[0] == 0) while(1);

		for(int i = 0; i < Z; i++)
		{
			x[edges[i]] = (a[i] * (c[nodes[0]] - (b.back() + b[0]))) + b[i]*2;

			assert(x[edges[i]] % 2 == 0);

			// cerr << i << " : " << nodes[i] << " : " << a[i] << ' ' << b[i] << "\n";
		}
	}

	for(int e = 1; e <= M; e++) 
		cout << x[e] << '\n';
}

• Subtask 1: 30 / 30
• Subtask 2: 44.074074074074076 / 70