POJ 2983 Is the Information Reliable? 差分约束

裸差分约束。

//#pragma comment(linker, "/STACK:1024000000,1024000000")

#include<cstdio>

#include<cstring>

#include<cstdlib>

#include<algorithm>

#include<iostream>

#include<sstream>

#include<cmath>

#include<climits>

#include<string>

#include<map>

#include<queue>

#include<vector>

#include<stack>

#include<set>

using namespace std;

typedef long long ll;

typedef unsigned long long ull;

typedef pair<int,int> pii;

#define pb(a) push(a)

#define INF 0x1f1f1f1f

#define lson idx<<1,l,mid

#define rson idx<<1|1,mid+1,r

#define PI  3.1415926535898

template<class T> T min(const T& a,const T& b,const T& c) {

    return min(min(a,b),min(a,c));

}

template<class T> T max(const T& a,const T& b,const T& c) {

    return max(max(a,b),max(a,c));

}

void debug() {

#ifdef ONLINE_JUDGE

#else

freopen("data.in","r",stdin);

   // freopen("d:\\out1.txt","w",stdout);

#endif

}

int getch() {

    int ch;

    while((ch=getchar())!=EOF) {

        if(ch!=‘ ‘&&ch!=‘\n‘)return ch;

    }

    return EOF;

}
struct Edge

{

     int from, to, dist;

};

const int maxn = 1111;

int n;

vector<int> g[maxn];

vector<Edge> edge;
void Init()

{

     for(int i = 1; i <= n; i++)

          g[i].clear();

     edge.clear();

}

void AddEdge(int u, int v, int w)

{

     edge.push_back((Edge){u, v, w});

     g[u].push_back(edge.size() - 1);

}
int inq[maxn];

int cnt[maxn];

int d[maxn];
bool SPFA()

{

     queue<int> q;

     for(int i=1; i<=n; i++)

     {

          inq[i] = true;

          cnt[i] = 0;

          d[i] = 0;

          q.push(i);

     }

     while(!q.empty())

     {

          int u = q.front(); q.pop();

          inq[u] = false;

          for(int i=0; i < g[u].size(); i++)

          {

               //cout<<g[u][i]<<endl;

               Edge &e = edge[ g[u][i] ];

               //cout<<" "<<e.from<<" "<<e.to<<" "<<e.dist<<endl;

               if(d[e.to] < d[u] + e.dist)

               {

                    d[e.to] = d[u] + e.dist;

                    inq[e.to] = true;

                    if(++cnt[e.to] > n) return 0;

                    q.push(e.to);

               }

          }

     }

     return 1;

}
int main()

{

     debug();

     int m;

     while(scanf("%d%d", &n, &m) != EOF)

     {

          Init();

          for(int i = 1; i <= m; i++)

          {

               char op = getch();

               if(op == ‘P‘)

               {

                    int u,v,x;

                    scanf("%d%d%d", &u, &v, &x);

                    AddEdge(u,v,x);

                    AddEdge(v,u,-x);

               }else

               {

                    int u,v;

                    scanf("%d%d", &u, &v);

                    AddEdge(v,u,1);

               }

          }

          //cout<<edge.size()<<endl;

         // for(int i=0; i<=n; i++)

         //      cout<<g[i].size()<<endl;

          int ans = SPFA();

          printf("%s\n", ans?"Reliable":"Unreliable");

     }

     return 0;

}

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