HDU4396

题意：s到e，最短时间且至少经过k条边

dis[ i ][ j ]:表示s到i至少经过了j条边的最少时间！

二维spfa

View Code

 1 #include<stdio.h>

 2 #include<string.h>

 3 #include<queue>

 4 #include<algorithm>

 5 #include<stdlib.h>

 6 using namespace std;

 7 const int maxn = 5005;

 8 const int maxm = 100005;

 9 const int inf = 9999999;

10 int n,m;

11 int ans;

12 struct node{

13     int u,val,next;

14 }edge[ maxm*2 ];

15 int head[ maxn ],cnt;

16 void init(){

17     cnt=0;

18     memset( head,-1,sizeof( head ));

19 }

20 void addedge( int a,int b,int c ){

21     edge[ cnt ].u=b;

22     edge[ cnt ].val=c;

23     edge[ cnt ].next=head[ a ];

24     head[ a ]=cnt++;

25 }

26 int dis[ maxn ][ 505 ],vis[ maxn ][ 505 ];//dis[i][j]:s到i经过j步的最少时间

27 struct node2{

28     int pos,num;

29 };

30 

31 

32 void spfa( int s,int e,int k ){

33     memset( vis,0,sizeof( vis ) );

34     //memset( dis,0x3f3f3f,sizeof( dis ));

35     for(int i=1;i<=n;i++)

36         for(int j=0;j<=k;j++)

37             dis[i][j]=inf;

38     queue<node2>q;

39     while(!q.empty())q.pop();

40     node2 now,next;

41     now.pos=s,now.num=0;

42     vis[ now.pos ][ now.num ]=1;

43     dis[ now.pos ][ now.num ]=0;

44     q.push( now );

45     ans=inf;

46     while( !q.empty() ){

47         now=q.front(),q.pop();

48         vis[now.pos][now.num]=0;

49         if( now.pos==e&&now.num==k ){

50             ans=min( ans,dis[e][k] );//return dis[e][k];

51         }

52         for( int i=head[ now.pos ];i!=-1;i=edge[i].next ){

53             next.pos=edge[i].u;

54             next.num=now.num+10;

55             if(next.num>=k)next.num=k;

56             if( next.num>=k )

57                 next.num=k;

58             if( dis[next.pos][next.num]>dis[now.pos][now.num]+edge[i].val ){

59                 dis[next.pos][next.num]=dis[now.pos][now.num]+edge[i].val;

60                 if( vis[next.pos][next.num]==0 ){

61                     vis[next.pos][next.num]=1;

62                     q.push(next);

63                 }

64             }

65         }

66     }

67     if( ans==inf )

68         ans=-1;

69 }

70 

71 int main(){

72     while( scanf("%d%d",&n,&m)!=EOF ){

73         init();

74         int a,b,c;

75         while( m-- ){

76             scanf("%d%d%d",&a,&b,&c);

77             addedge( a,b,c );

78             addedge( b,a,c );

79         }

80         int s,e,k;

81         scanf("%d%d%d",&s,&e,&k);

82         spfa( s,e,k );

83         printf("%d\n",ans);

84     }

85     return 0;

86 }