BZOJ——1614: [Usaco2007 Jan]Telephone Lines架设电话线

 1 #include <cstdio>
 2 #include <queue>
 3 
 4 #define min(a,b) (a<b?a:b)
 5 
 6 inline void read(int &x)
 7 {
 8     x=0; register char ch=getchar();
 9     for(; ch>‘9‘||ch<‘0‘; ) ch=getchar();
10     for(; ch>=‘0‘&&ch<=‘9‘; ch=getchar()) x=x*10+ch-‘0‘;
11 }
12 const int M(10005);
13 const int N(1005);
14 int n,k,p;
15 int head[N],sumedge;
16 struct Edge {
17     int v,next,w;
18     Edge(int v=0,int next=0,int w=0):v(v),next(next),w(w){}
19 }edge[M<<1];
20 inline void ins(int u,int v,int w)
21 {
22     edge[++sumedge]=Edge(v,head[u],w),head[u]=sumedge;
23     edge[++sumedge]=Edge(u,head[v],w),head[v]=sumedge;
24 }
25 
26 bool inq[N];
27 int dis[N];
28 std::queue<int>que;
29 int L,R,Mid,ans=-1;
30 inline bool check(int lim)
31 {
32     for(int i=1; i<=n; ++i)
33         dis[i]=0x3f3f3f3f,inq[i]=0;
34     for(; !que.empty(); ) que.pop();
35     int cnt=0; que.push(1); dis[1]=0;
36     for(int u,v; !que.empty(); )
37     {
38         u=que.front(); que.pop(); inq[u]=0;
39         for(int i=head[u]; i; i=edge[i].next)
40         {
41             v=edge[i].v;
42             cnt=(edge[i].w>lim);
43             if(dis[v]>dis[u]+cnt)
44             {
45                 dis[v]=dis[u]+cnt;
46                 if(!inq[v]) inq[v]=1,que.push(v);
47             }
48         }
49     }
50     return dis[n]<=k;
51 }
52 
53 int Presist()
54 {
55     read(n),read(p),read(k);
56     for(int u,v,w,i=1; i<=p; ++i)
57         read(u),read(v),read(w),ins(u,v,w),R=R>w?R:w;;
58     for(; L<=R; )
59     {
60         Mid=L+R>>1;
61         if(check(Mid))
62         {
63             ans=Mid;
64             R=Mid-1;
65         }
66         else L=Mid+1;
67     }
68     printf("%d\n",ans);
69     return 0;
70 }
71 
72 int Aptal=Presist();
73 int main(int argc,char**argv){;}