spfa代码

先来贴一下,,虽然不是自己写的 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<queue>

#define Maxn 100

#define Maxm 10000
#define Max 10000
using namespace std;

int used[Maxn],outqueue[Maxn],head[Maxn],low[Maxn],n,m;

struct Edge
{
       int to,w,next;
}edge[Maxm];

bool SPFA (int start)
{
     queue a;
     used[start] = 1;
     low[start] = 0;
     a.push(start);
     while (!a.empty())
     {
           int top = a.front();
           a.pop();
           outqueue[top]++;
           if (outqueue[top] > n) return false;
           for (int k = head[top]; k!= -1; k = edge[k].next)
           {
               if (low[edge[k].to] > low[top] + edge[k].w)
                  low[edge[k].to] = low[top] + edge[k].w;
               if (!used[edge[k].to])
               {
                   used[edge[k].to] = 1;
                   a.push(edge[k].to);
               }
           }
     }
     return true;
}
    
int main()
{
    while (scanf ("%d%d", &n ,&m) != EOF)
    {
          memset (used, 0 ,sizeof(used));
          memset (head, -1 ,sizeof(head));
          memset (outqueue, 0 ,sizeof(outqueue));
          memset (low, Max, sizeof(low));
          int k = 0;
          while (m--)
          {
                int a,b,w;
                scanf ("%d%d%d", &a, &b, &w);
                edge[k].to = b;
                edge[k].w = w;
                edge[k].next = head[a];
                head[a] = k++;
          }
          if (SPFA(1))
             printf ("%d ", low[n]);
          else
             printf ("不存在最短 ");
    }
}