2017-2018 ACM-ICPC, NEERC, Southern Subregional Contest G. Orientation of Edges

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最新推荐文章于 2020-07-16 19:21:52 发布 · 887 阅读

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给定一个包含有向和无向边的图，起点为s，求最大化和最小化从s可达的节点数的边定向方案。输入包含节点数、边数和起点，输出两个方案及每个方案可达的节点数，每个方案中无向边的方向。

G. Orientation of Edges
time limit per test3 seconds
memory limit per test256 megabytes
inputstandard input
outputstandard output
Vasya has a graph containing both directed (oriented) and undirected (non-oriented) edges. There can be multiple edges between a pair of vertices.

Vasya has picked a vertex s from the graph. Now Vasya wants to create two separate plans:

to orient each undirected edge in one of two possible directions to maximize number of vertices reachable from vertex s;
to orient each undirected edge in one of two possible directions to minimize number of vertices reachable from vertex s.
In each of two plans each undirected edge must become directed. For an edge chosen directions can differ in two plans.

Help Vasya find the plans.

Input
The first line contains three integers n, m and s (2 ≤ n ≤ 3·105, 1 ≤ m ≤ 3·105, 1 ≤ s ≤ n) — number of vertices and edges in the graph, and the vertex Vasya has picked.

The following m lines contain information about the graph edges. Each line contains three integers ti, ui and vi (1 ≤ ti ≤ 2, 1 ≤ ui, vi ≤ n, ui ≠ vi) — edge type and vertices connected by the edge. If ti = 1 then the edge is directed and goes from the vertex ui to the vertex vi. If ti = 2 then the edge is undirected and it connects the vertices ui and vi.

It is guaranteed that there is at least one undirected edge in the graph.

Output
The first two lines should describe the plan which maximizes the number of reachable vertices. The lines three and four should descri