Candies(差分约束系统)

http://poj.org/problem?id=3159

思路：用O(V+ElogV)的Dijkstra算法求1到n的最短路。即用优先队列优化Dijkstra算法。

 #include <stdio.h>
 #include <queue>
 #include <string.h>
 using namespace std;
 const int maxn=;
 const int maxm=;
 struct node
 {
     int u,v,w;
     int  next;
 } edge[maxm];
 struct pot
 {
     int v,w;
     pot(int v = ,int w = ):v(v),w(w) {}
     bool operator < (const pot &a)const
     {
         return w > a.w;
     }
 };
 int n,m;
 int head[maxn],vis[maxn],dis[maxn],cnt;
 void add(int u,int v,int w)
 {
     edge[cnt].u = u;
     edge[cnt].v = v;
     edge[cnt].w = w;
     edge[cnt].next = head[u];
     head[u] = cnt++;
 }
 void Dijkstra(int s)
 {
     memset(vis,,sizeof(vis));
     memset(dis,,sizeof(dis));
     dis[s] = ;
     priority_queue<pot>q;
     q.push(pot(s,dis[s]));
     for(int i = ; i < n; i++)
     {
         while(!q.empty()&&vis[q.top().v])//去掉队首被标记的点
             q.pop();
         if (q.empty()) break;
         pot pre = q.top();//取出队首的点，即权值最小的点
         q.pop();
         vis[pre.v] = ;//标记
         for (int j = head[pre.v]; j !=-; j= edge[j].next)//找出pre的所有连接点
         {
             int v = edge[j].v;
             if (!vis[v] && dis[pre.v]+edge[j].w < dis[v])//更新所有点到源点的距离
             {
                 dis[v] = dis[pre.v]+edge[j].w;
                 q.push(pot(v,dis[v]));//将更新后的点与权值入队列
             }
         }

     }

 }
 int main()
 {
     int u,v,w;
     cnt = ;
     scanf("%d %d",&n,&m);
     memset(head,-,sizeof(head));
     for (int i = ; i < m; i++)
     {
         scanf("%d %d %d",&u,&v,&w);
         add(u,v,w);
     }
     Dijkstra();
     printf("%d\n",dis[n]);
     return ;
 }