POJ 3259 SPFA

这题让我英语太受打击了，题意难懂，读懂题意纸老虎。

算法：

1.题意本质就是判断是否存在负权回路。

2.SPFA，一个点入队大于等于N次，就说明它存在负权回路。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <queue>
#include <iostream>
using namespace std;
#define MAXN 100100


struct Edge
{
  int u, next, val;
  Edge() {}
  Edge( int v , int Next ,int Val): u(v),next(Next), val(Val) { }      
}edge[MAXN];

const int inf = 0x7f7f7f7f;
int head[MAXN],dis[MAXN], visit[MAXN], size, hash[MAXN];

int N, M, W, T;

struct node
{
  int ID,dis;
};

void init( )
{
  for( int i = 0; i <= N; i++)
  {
       head[i] = -1;
       visit[i] = 0;
       dis[i] = inf;
       hash[i] = 0;
  }
  size = 0;
       
}

void AddEdge( int u, int v, int val, int num)
{
   edge[size] = Edge( v, head[u], val);
   head[u] = size++;
   if( !num )
   {
    edge[size] = Edge( u, head[v], val);
    head[v] = size++;
   }
     
}


void SPFA( )
{
   queue<node>q;
   node p;
   p.ID = 1;
   p.dis = 0;
   q.push(p);
   dis[1] = 0;
   while( !q.empty( ))
   {  
       p = q.front( );
       q.pop();
       int v = p.ID;
       int wx = dis[v];
       visit[v] = 0;
       for( int e = head[v]; e != -1; e = edge[e].next)
       {  
          int u = edge[e].u;
          int w = edge[e].val;
          if( dis[u] > wx + w )
          {
               dis[u] = wx + w;
               if( !visit[u] )
               {    
                 p.ID = u;
                 p.dis = dis[u];
                 visit[u] = 1;
                 q.push( p );
                 hash[u]++;
               }
               if( hash[u] >= N )
               {
                   puts("YES");
                   return ;    
                   
               }
               
                
          }  
            
       }
   }
   puts("NO");
} 
        
int main( )
{
  int a, b, c;
  scanf("%d", &T);
  while(T--)
  {
     scanf("%d%d%d", &N,  &M, &W);
     init( );          
     for( int i = 1; i <= M; i++)
     {
        scanf("%d%d%d", &a, &b, &c);
        AddEdge( a, b, c, 0);   
     }
     for( int i = 1; i <= W; i++)
     { 
        scanf("%d%d%d", &a, &b, &c);
        AddEdge( a, b, -c, 1);    
     }
     SPFA( );
            
  }    
  return 0;    
}