杭电1874----畅通工程续

Posted 2020-10-01 Jeson

  1 /*
  2 最短路径问题
  3 可利用Bellman-Ford算法或者Dijktra算法求解。
  4  */
  5 #include <iostream>
  6 #include <cstring>
  7 #include <vector>
  8 #include <queue>
  9 using namespace std;
 10 const int maxn = 205;
 11 const int inf = 0x3f3f3f3f;
 12 struct edge
 13 {
 14     edge(int x,int y)
 15     {
 16         v = x;
 17         len = y;
 18     }
 19     int v, len;
 20 };
 21 vector<edge> e[maxn];
 22 int dis[maxn], inq[maxn];
 23 /*int spfa(int s, int t)        //Bellman-Ford
 24 {
 25     queue<int> q;
 26     memset(inq, 0, sizeof inq);
 27     memset(dis, 0x3f, sizeof dis);
 28     dis[s] = 0; inq[s] = true;
 29     q.push(s);
 30     while (!q.empty())
 31     {
 32         int n = q.front();
 33         q.pop();
 34         for (int i = 0; i < e[n].size(); ++i)
 35         {
 36             int v = e[n][i].v, len = e[n][i].len;
 37             if (dis[v] > dis[n] + len)
 38             {
 39                 dis[v] = dis[n] + len;
 40                 if (!inq[v]) {q.push(v); inq[v] = true;}//判断队列是否存在该节点，存在无须加入重复判断
 41             }
 42         }
 43         inq[n] = false;
 44     }
 45     return dis[t]==inf?-1:dis[t];
 46 }*/
 47 int dijktra(int s,int t)        //Dijktra
 48 {
 49     memset(dis,0x3f,sizeof dis);
 50     dis[s] = 0;
 51     priority_queue< pair<int,int> > q;
 52     q.push(make_pair(-dis[s],s));
 53     while(!q.empty())
 54     {
 55         int x = q.top().first,y = q.top().second;
 56         q.pop();
 57         if(dis[y] < x) continue;//dis[y] < x表示前面已经储存过更优路径，无需再次更新y后面的节点
 58         for(int i = 0; i < e[y].size(); ++i)
 59         {
 60             int v = e[y][i].v,len = e[y][i].len;
 61             if(dis[v] > dis[y] + len)
 62             {
 63                 dis[v] = dis[y] + len;
 64                 q.push(make_pair(-dis[v],v));
 65             }
 66         }
 67     }
 68     return dis[t]==inf?-1:dis[t];
 69 }
 70 int main()
 71 {
 72     int n, m;
 73     while (cin >> n >> m)
 74     {
 75         for(int i = 0; i < n; ++i)
 76             e[i].clear();
 77         for (int i = 0; i < m; ++i)
 78         {
 79             int x, y, d;
 80             cin >> x >> y >> d;
 81             e[x].push_back(edge(y,d));
 82             e[y].push_back(edge(x,d));
 83         }
 84         int s, t;
 85         cin >> s >> t;
 86         //int ans = spfa(s,t);
 87         int ans = dijktra(s, t);
 88         cout << ans << endl;
 89     }
 90 }
 91 /*
 92 3 3
 93 0 1 1
 94 0 2 3
 95 1 2 1
 96 0 2
 97 3 1
 98 0 1 1
 99 1 2
100 
101  */