【bzoj1614】[Usaco2007 Jan]Telephone Lines架设电话线

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cstdlib>
 5 #include<cmath>
 6 #include<ctime>
 7 #include<algorithm>
 8 using namespace std;
 9 struct node{int y,next,v;}e[20010];
10 int n,m,k,len,ans,Link[1010],vis[1010],dis[1010],q[2000100];
11 inline int read()
12 {
13     int x=0,f=1;  char ch=getchar();
14     while(!isdigit(ch))  {if(ch==‘-‘)  f=-1;  ch=getchar();}
15     while(isdigit(ch))  {x=x*10+ch-‘0‘;  ch=getchar();}
16     return x*f;
17 }
18 void insert(int xx,int yy,int vv)
19 {
20     e[++len].next=Link[xx];
21     Link[xx]=len;
22     e[len].y=yy;
23     e[len].v=vv;
24 }
25 int check(int x)
26 {
27     memset(dis,40,sizeof(dis));
28     int head=0,tail=1,s;  q[1]=1;  vis[1]=1;  dis[1]=0;
29     while(++head<=tail)
30     {
31         int now=q[head];
32         for(int i=Link[now];i;i=e[i].next)
33         {
34             if(e[i].v>x)  s=dis[now]+1;
35             else s=dis[now];
36             if(s<dis[e[i].y])
37             {
38                 dis[e[i].y]=s;
39                 if(!vis[e[i].y])
40                 {
41                     q[++tail]=e[i].y;
42                     vis[e[i].y]=1;
43                 }
44             }
45         }
46         vis[now]=0;
47     }
48     return dis[n]<=k;
49 }
50 int main()
51 {
52     n=read();  m=read();  k=read();
53     for(int i=1;i<=m;i++)
54     {
55         int x=read(),y=read(),v=read();
56         insert(x,y,v);  insert(y,x,v);
57     }
58     int l=0,r=1000000;
59     while(l<=r)
60     {
61         int mid=(l+r)/2;
62         if(check(mid))  {ans=mid;  r=mid-1;}
63         else l=mid+1;
64     }
65     printf("%d\n",ans);
66     return 0;
67 }