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 }

 

posted @ 2013-02-21 22:03  xxx0624  阅读(290)  评论(0)  编辑  收藏  举报