poj3268 最短路

  1 //Accepted    1124 KB    0 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 = 100005;
 16 const long long inf = 100000000000000LL;
 17 struct node
 18 {
 19     int u,v,c;
 20     node()
 21     {
 22 
 23     }
 24     node(int u,int v,int c):u(u),v(v),c(c)
 25     {
 26 
 27     }
 28 }p[imax_e],rp[imax_e];
 29 int head[imax_n];
 30 int next[imax_e];
 31 int rhead[imax_n];
 32 int rnext[imax_e];
 33 int e;
 34 int re;
 35 long long dis[imax_n];
 36 long long cost[imax_n];
 37 bool vis[imax_n];
 38 int n,m,x;
 39 void init()
 40 {
 41     e=0;
 42     re=0;
 43     memset(head,-1,sizeof(head));
 44     memset(next,-1,sizeof(next));
 45     memset(rhead,-1,sizeof(rhead));
 46     memset(rnext,-1,sizeof(rnext));
 47 }
 48 void addEdge(int u,int v,int c)
 49 {
 50     p[e]=node(u,v,c);
 51     next[e]=head[u];
 52     head[u]=e++;
 53 }
 54 void raddEdge(int u,int v,int c)
 55 {
 56     rp[re]=node(u,v,c);
 57     rnext[re]=rhead[u];
 58     rhead[u]=re++;
 59 }
 60 queue<int > q;
 61 int cnt[imax_n];
 62 bool relax(int u,int v,int c)
 63 {
 64     if (dis[v]>dis[u]+c)
 65     {
 66         dis[v]=dis[u]+c;
 67         return true;
 68     }
 69     return false;
 70 }
 71 bool spfa(int src,int h[],int nt[],node p[])
 72 {
 73     memset(cnt,0,sizeof(cnt));
 74     while (!q.empty()) q.pop();
 75     memset(vis,0,sizeof(vis));
 76     q.push(src);
 77     vis[src]=true;
 78     for (int i=1;i<=n;i++)
 79     dis[i]=inf;
 80     dis[src]=0;
 81     while (!q.empty())
 82     {
 83         int pre=q.front();
 84         q.pop();
 85         vis[pre]=false;
 86         for (int i=h[pre];i+1;i=nt[i])
 87         {
 88             if (relax(pre,p[i].v,p[i].c) && !vis[p[i].v])
 89             {
 90                 if ((++cnt[p[i].v])>n) return false;
 91                 vis[p[i].v]=true;
 92                 q.push(p[i].v);
 93             }
 94         }
 95     }
 96     return true;
 97 }
 98 long long slove()
 99 {
100     int u,v,c;
101     init();
102     for (int i=1;i<=m;i++)
103     {
104         scanf("%d%d%d",&u,&v,&c);
105         addEdge(u,v,c);
106         raddEdge(v,u,c);
107     }
108     long long ans=0;
109     spfa(x,head,next,p);
110     for (int i=1;i<=n;i++)
111     {
112         cost[i]=dis[i];
113         //printf("dis[%d]=%d\n",i,dis[i]);
114     }
115     spfa(x,rhead,rnext,rp);
116     for (int i=1;i<=n;i++)
117     {
118         //printf("cost[%d]=%d\n",i,dis[i]);
119         if (cost[i]+dis[i]>ans)
120         ans=cost[i]+dis[i];
121     }
122     return ans;
123 }
124 int main()
125 {
126     while (scanf("%d%d%d",&n,&m,&x)!=EOF)
127     {
128         __int64 ans=slove();
129         printf("%I64d\n",ans);
130     }
131     return 0;
132 }