优化的Bellman-Ford——SPFA

优化的Bellman-Ford——SPFA

SPFA的基本思路是：只有被修改过最短路的顶点，才有可能导致修改与它邻接的顶点的最短路。于是很容易想到用一个队列维护。
以下是我的代码：

#include < stdio.h >
#define  min(a,b) (a<b?a:b)
const   long  maxn = 507 ;
const   long  INF = 100000007 ;
typedef  struct
{
     long  front,rear,count,item[maxn];
}queue;
void  clear(queue  & q)
{
    q.count = 0 ;
    q.front = 0 ;
    q.rear =- 1 ;
}
bool  empty(queue  & q)
{
     return  (q.count == 0 );
}
void  push(queue  & q, long  x)
{
    q.rear ++ ;
    q.item[q.rear] = x;
    q.count ++ ;
}
long  pop(queue  & q)
{
     long  x = q.item[q.front];
    q.front ++ ;
    q.count -- ;
     return  x;
}
//   Queue
typedef  struct  EDGE_NODE
{
     long  u,v,w;
     struct  EDGE_NODE  * next;
}edge_node;
long  n,m,d[maxn];
edge_node  * a[maxn];
//   Var
void  insert( long  begin, long  end, long  weight)
{
    edge_node  * p = new  edge_node;
    p -> u = begin;p -> v = end;p -> w = weight;
    p -> next = a[begin] -> next;
    a[begin] -> next = p;
}
bool  bellman_ford( long  s)
{
     bool   in [maxn];
     long  in_num[maxn];
    queue q;clear(q);
    edge_node  * p;
     for ( long  i = 1 ;i <= n;i ++ )
    {
       d[i] = (i == s ? 0 :INF);
        in [i] = false ;
       in_num[i] = 0 ;
    }
    push(q,s);
     in [s] = true ;
    in_num[s] ++ ;
     while ( ! empty(q))
    {
        long  i = pop(q); in [i] = false ;
        for (p = a[i] -> next;p;p = p -> next)
       {
           long  j = p -> v;
           if (d[i] + p -> w < d[j])
          {
             d[j] = d[i] + p -> w;
              if ( ! in [j])
             {
                push(q,j);
                 in [j] = true ;
                in_num[j] ++ ;
                 if (in_num[j] > n)  return   false ;
             }
          }
       }
    }
     return   true ;
}
int  main()
{
     // *
    freopen( " data.in " , " r " ,stdin);
    freopen( " data.out " , " w " ,stdout);
     // */
    scanf( " %ld%ld " , & n, & m);
     for ( long  i = 1 ;i <= n;i ++ )
    {
       a[i] = new  edge_node;
       a[i] -> next = NULL;
    }
     for ( long  i = 1 ;i <= m;i ++ )
    {
        long  a,b,w;
       scanf( " %ld%ld%ld " , & a, & b, & w);
       insert(a,b,w);
       insert(b,a,w);
    }
     if (bellman_ford( 1 ))
    {
        for ( long  i = 1 ;i <= n;i ++ ) printf( " %ld  " ,d[i]);
       putchar( ' \n ' );
    }
     else  printf( " Error\n " );
return   0 ;
}