Description
Bessie is out in the field and wants to get back to the barn to get as much sleep as possible before Farmer John wakes her for the morning milking. Bessie needs her beauty sleep, so she wants to get back as quickly as possible.
Farmer John‘s field has N (2 <= N <= 1000) landmarks in it,
uniquely numbered 1..N. Landmark 1 is the barn; the apple tree grove in
which Bessie stands all day is landmark N. Cows travel in the field
using T (1 <= T <= 2000) bidirectional cow-trails of various
lengths between the landmarks. Bessie is not confident of her navigation
ability, so she always stays on a trail from its start to its end once
she starts it.Given the trails between the landmarks, determine the minimum
distance Bessie must walk to get back to the barn. It is guaranteed
that some such route exists.
Input
* Line 1: Two integers: T and N
* Lines 2..T+1: Each line describes a trail as three space-separated
integers. The first two integers are the landmarks between which the
trail travels. The third integer is the length of the trail, range
1..100.
Output
* Line 1: A single integer, the minimum distance that Bessie must travel to get from landmark N to landmark 1
Sample Input
5 5 1 2 20 2 3 30 3 4 20 4 5 20 1 5 100
Sample Output
90
Dijkstra模板题
Code:
1 #include<cstdio>
2 #include<iostream>
3 #include<algorithm>
4 #include<cstring>
5 #include<queue>
6 #include<vector>
7 #include<set>
8 #include<map>
9 #include<string>
10
11 using namespace std;
12 #define INF 0x3f3f3f3f
13 const int maxn = 2000 + 5;
14
15 struct Edge {
16 int from, to, dist;
17 };
18
19 struct Node {
20 int d, u;
21 bool operator < (const Node& rhs) const {
22 return d > rhs.d;
23 }
24 };
25
26 struct Dijkstra {
27 int n, m;
28 vector<Edge> edges; //保存边信息
29 vector<int> G[maxn]; //出边表
30 int d[maxn];
31 bool done[maxn];
32
33 void init(int n) {
34 this->n = n;
35 memset(done, 0, sizeof(done));
36 memset(d, INF, sizeof(d));
37 for (int i = 0; i <= n; ++i)
38 G[i].clear();
39 edges.clear();
40 }
41
42 void AddEdge(int from, int to, int dist) {
43 edges.push_back((Edge){from, to, dist});
44 m = edges.size();
45 G[from].push_back(m-1);
46 }
47
48 void dijkstra(int s) {
49 priority_queue<Node> Q;
50 d[s] = 0;
51 Q.push((Node){d[s], s});
52 while(!Q.empty()) {
53 Node x = Q.top(); Q.pop();
54 int u = x.u;
55 if (done[u]) continue;
56 done[u] = true;
57 int len = G[u].size();
58 for (int i = 0; i < len; ++i) {
59 Edge &e = edges[G[u][i]];
60 if (d[e.to] > d[u] + e.dist) {
61 d[e.to] = d[u] + e.dist;
62 Q.push((Node){d[e.to], e.to});
63 }
64 }
65 }
66 }
67
68 };
69
70 Dijkstra di;
71
72 int main() {
73 int n, m, a, b, c;
74 while(cin>>m>>n) {
75 di.init(n);
76 while(m--) {
77 cin>>a>>b>>c;
78 di.AddEdge(a, b, c);
79 di.AddEdge(b, a, c);
80 }
81 di.dijkstra(1);
82 cout<<di.d[n]<<endl;
83 }
84
85 return 0;
86 }