poj2387 spfa求最短路

  1 //Accepted    4688 KB    63 ms
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <iostream>
  5 #include <queue>
  6 #include <cmath>
  7 #include <algorithm>
  8 using namespace std;
  9 /**
 10   * This is a documentation comment block
 11   * 如果有一天你坚持不下去了，就想想你为什么走到这儿！
 12   * @authr songt
 13   */
 14 const int imax_n = 1005;
 15 const int imax_e = imax_n*imax_n;
 16 const int inf=100000000;
 17 int head[imax_n];
 18 int next[imax_e];
 19 struct node
 20 {
 21     int u,v,c;
 22     node()
 23     {
 24 
 25     }
 26     node(int u,int v,int c):u(u),v(v),c(c)
 27     {
 28 
 29     }
 30 }p[imax_e];
 31 int e;
 32 void init()
 33 {
 34     memset(head,-1,sizeof(head));
 35     memset(next,-1,sizeof(next));
 36     e=0;
 37 }
 38 void addEdge(int u,int v,int c)
 39 {
 40     p[e]=node(u,v,c);
 41     next[e]=head[u];
 42     head[u]=e++;
 43 }
 44 int dis[imax_n];
 45 bool vis[imax_n];
 46 int cnt[imax_n];
 47 int n,m;
 48 queue<int > q;
 49 bool relax(int u,int v,int c)
 50 {
 51     if (dis[v]>dis[u]+c)
 52     {
 53         dis[v]=dis[u]+c;
 54         return true;
 55     }
 56     return false;
 57 }
 58 bool spfa(int src)
 59 {
 60     while (!q.empty()) q.pop();
 61     memset(vis,false,sizeof(vis));
 62     memset(cnt,0,sizeof(cnt));
 63     for (int i=0;i<=n;i++)
 64     dis[i]=inf;
 65     dis[src]=0;
 66     q.push(src);
 67     vis[src]=true;
 68     while (!q.empty())
 69     {
 70         int pre=q.front();
 71         q.pop();
 72         vis[pre]=false;
 73         for (int i=head[pre];i+1;i=next[i])
 74         {
 75             if (relax(pre,p[i].v,p[i].c) && !vis[p[i].v])
 76             {
 77                 if ((++cnt[p[i].v])>n) return false;
 78                 q.push(p[i].v);
 79                 vis[p[i].v]=true;
 80             }
 81         }
 82     }
 83     return true;
 84 }
 85 int main()
 86 {
 87     while (scanf("%d%d",&m,&n)!=EOF)
 88     {
 89         init();
 90         int u,v,c;
 91         for (int i=0;i<m;i++)
 92         {
 93             scanf("%d%d%d",&u,&v,&c);
 94             addEdge(u,v,c);
 95             addEdge(v,u,c);
 96         }
 97         spfa(n);
 98         printf("%d\n",dis[1]);
 99     }
100     return 0;
101 }