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 */
