POJ 2983

POJ 2983 Is the information reliable?

SPFA+差分约束练习题。

注意事项：

P:             //dis[a] - dis[b] = c;
                //dis[a] - dis[b] <= c;
                //dis[b] - dis[a] <= -c;

V:            //dis[a] - dis[b] >= 1;
               //dis[b] - dis[a] <= -1;

bellman-ford的话不用加超级源，但是SPFA要，因为给的图可能不连通。

deg表示入队的次数，网上有些代码将deg表示成松弛的次数，提交也过了，但是感觉是不对的（确实也很难构造出这样的数据）。

这是我的代码，可以作为SPFA模板

#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>

using std::memset;
using std::queue;
using std::vector;

const int MAX = 1005;
const int INF = 99999999;

int n,m;
queue<int> q;

struct edge
{
	int to,v;
	edge(int _to,int _v)
	{
		to = _to;
		v = _v;
	}
};
vector<edge> graph[MAX];

bool spfa()
{
	int dis[MAX];
	int vis[MAX];
	int deg[MAX];

	for(int i = 0; i < MAX; i++) dis[i] = INF;
	memset(vis,0,sizeof(vis));
	memset(deg,0,sizeof(deg));

	dis[0] = 0;
	q.push(0);
	deg[0]++;

	while(q.empty() == false)
	{
		int from = q.front();
		q.pop();
		vis[from] = false;

		for(int i = 0 ; i < graph[from].size(); i++)
		{
			int to = graph[from][i].to;
			int v = graph[from][i].v;

			if(dis[to] > dis[from] + v)
			{
				dis[to] = dis[from] + v;
				if(!vis[to])
				{
					q.push(to);
					vis[to] = 1;

					deg[to]++;
					if(deg[to] >= n)
					return false;
				}

			}
		}
	}
	return true;
}

int main()
{
	while(scanf("%d%d",&n, &m)!=EOF)
	{
		//init;
		for(int i = 0 ; i < MAX; i++)
		{
			graph[i].clear();
		}
		while(!q.empty()) q.pop();

		while(m--)
		{
			char op[2];
			scanf("%s", op);
			if(op[0] == 'P')
			{
				int a,b,c;
				scanf("%d%d%d",&a,&b,&c);
				graph[a].push_back(edge(b,-c));
				graph[b].push_back(edge(a,c));
				//dis[a] - dis[b] = c;
				//dis[a] - dis[b] <= c;
				//dis[b] - dis[a] <= -c;
			}
			else
			{
				int a,b;
				scanf("%d%d",&a,&b);
				graph[a].push_back(edge(b,-1));
				//dis[a] - dis[b] >= 1;
				//dis[b] - dis[a] <= -1;
			}
		}

		//super source;
		for(int i = 0 ; i <= n; i++)
		{
			graph[0].push_back(edge(i,0));
		}

		if(spfa())
		{
			printf("Reliable\n");
		}
		else
		{
			printf("Unreliable\n");
		}
	}
}