【POJ 2983】 Is the information reliable？

【题目链接】

             点击打开链接

【算法】

         差分约束系统，SPFA判负环

【代码】

         

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cerrno>
#include <clocale>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <limits>
#include <list>
#include <map>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <utility>
#include <vector>
#include <cwchar>
#include <cwctype>
#include <stack>
#include <limits.h>
using namespace std;
#define MAXN 1010
#define MAXM 200010

struct Edge
{
        int to,w,nxt;
} e[MAXM];
int i,n,m,a,b,c,tot;
int dis[MAXN],head[MAXN];
char opt[5];

inline void add(int u,int v,int w)
{
        tot++;
        e[tot] = (Edge){v,w,head[u]};
        head[u] = tot;
}
inline bool spfa()
{
        int i,cur,v,w;
        queue<int> q;
        static bool inq[MAXN];
        static int cnt[MAXN];
        for (i = 1; i <= n; i++)
        {
                dis[i] = 0;
                q.push(i);
                inq[i] = true;
                cnt[i] = 1;
        }
        while (!q.empty())
        {
                cur = q.front();
                q.pop();
                inq[cur] = false;
                for (i = head[cur]; i; i = e[i].nxt)
                {
                        v = e[i].to;
                        w = e[i].w;
                        if (dis[cur] + w > dis[v])
                        {    
                                dis[v] = dis[cur] + w;
                                if (!inq[v])
                                {
                                        inq[v] = true;
                                        cnt[v]++;
                                        if (cnt[v] > n) return false;
                                        q.push(v);
                                }
                        }
                }
        }
        return true;
}
int main() 
{
        
        while (scanf("%d",&n) != EOF && n)
        {
                tot = 0;
                for (i = 1; i <= n; i++)     head[i] = 0;
                scanf("%d",&m);
                while (m--)
                {
                        scanf("%s",&opt);
                        if (strcmp(opt,"P") == 0)
                        {
                                scanf("%d%d%d",&a,&b,&c);
                                add(b,a,c);
                                add(a,b,-c);    
                        } else
                        {
                                scanf("%d%d",&a,&b);
                                add(b,a,1);
                        }    
                }        
                if (spfa()) printf("Reliable
");
                else printf("Unreliable
");
        }
        
        return 0;
    
}