hdu_1874

很直白的最短路，dijkstra。每次总是以距离source最近的点向外扩展（这样保证对任意一点n，到达n时总是最短距离）。从而到达sink时是最短距离。

 1 #include<iostream>

 2 #include<queue>

 3 #include<cstdio>

 4 #include<cstring>

 5 #include<vector>

 6 #define MAXN 222

 7 struct edge {

 8     int k,w;

 9     bool operator < (const edge &b)const//the order to sort elements in priority queue

10     {

11         return w > b.w;

12     }

13     edge(int kk = 0, int ww = 0)// Constructor

14     {

15         k = kk;

16         w = ww;

17     }

18 };

19 int N, M, A, B, X, S, T;

20 std::vector< std::vector<edge> > G;//a vector in a vector

21 //while you use vector , you don't have to create a 2d array, avoid wasting the memory.

22 bool vis[MAXN];

23 

24 int dijkstra(int s, int t)

25 {

26     std::priority_queue<edge> q;

27     edge head(s,0),node;

28     q.push(head);

29     while(q.empty()==false) {

30         head = q.top();//get the element at the front of the priority queue

31         q.pop();//the delete it

32         vis[head.k] = true;//a tag ,this element has been visited, we have get the shortest way from source to it

33         if(head.k == t)

34             return head.w;

35         for(int i = 0; i<G[head.k].size(); i++) {//

36             node.k = G[head.k][i].k;

37             if(vis[node.k]==true)//if the point has been reached , skip it.

38                 continue;

39             node.w = G[head.k][i].w + head.w;

40              q.push(node);//the newly extended point

41         }

42     }

43     return -1;//can not find a way till every element have been visited.

44 // So there is no way from source to sink

45 }

46 

47 int main()

48 {

49 //    freopen("in.txt","r",stdin);

50     while(~scanf("%d%d",&N,&M)) {

51         memset(vis,false,sizeof(vis));

52         G.clear();

53         G.resize(MAXN);

54         while(M--) {

55             scanf("%D%D%D",&A,&B,&X);

56             edge temp;

57             temp.k = B;

58             temp.w = X;

59             G[A].push_back(temp);//two-way road here

60             temp.k = A;

61             G[B].push_back(temp);

62         }

63         scanf("%d%d",&S,&T);

64         printf("%d\n",dijkstra(S, T));

65     }

66 }