BZOJ_1614_ [Usaco2007_Jan]_Telephone_Lines_架设电话线_(二分+最短路_Dijkstra/Spfa)

描述

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http://www.lydsy.com/JudgeOnline/problem.php?id=1614

分析

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类似POJ_3662_Telephone_Lines_(二分+最短路)

Dijkstra:

 #include <bits/stdc++.h>
 using namespace std;

 const int maxn=+,maxm=+,INF=<<;
 int n,m,k,ect;
 int hd[maxn],f[maxm],d[maxn];
 bool vis[maxn];
 struct edge{
     int to,w,next;
     edge(int to=,int w=,int next=):to(to),w(w),next(next){}
     bool operator < (const edge &a) const { return w>a.w; }
 }g[maxm<<];
 inline int read(int &x){ x=;int k=;char c;for(c=getchar();c<''||c>'';c=getchar())if(c=='-')k=-;for(;c>=''&&c<='';c=getchar())x=x*+c-'';return x*=k; }
 inline void add_edge(int u,int v,int w){
     g[++ect]=edge(v,w,hd[u]); hd[u]=ect;
     g[++ect]=edge(u,w,hd[v]); hd[v]=ect;
 }
 inline bool C(int x){
     for(int i=;i<=n;i++) d[i]=INF, vis[i]=false;
     d[]=;
     priority_queue <edge> q;
     q.push(edge(,,));
     while(!q.empty()){
         int u=q.top().to; q.pop();
         if(vis[u]) continue;
         vis[u]=true;
         for(int i=hd[u];i;i=g[i].next){
             int v=g[i].to,duv=g[i].w>x?:;
             if(d[v]>d[u]+duv){
                 d[v]=d[u]+duv;
                 q.push(edge(v,d[v],));
             }
         }
     }
     return d[n]<=k;
 }
 inline int bsearch(int l,int r){
     if(!C(f[r])) return-;
     while(l<r){
         int mid=l+(r-l)/;
         if(C(f[mid])) r=mid;
         else l=mid+;
     }
     return f[l];
 }
 int main(){
     read(n); read(m); read(k);
     for(int i=,u,v,w;i<=m;i++){
         read(u); read(v); read(w);
         add_edge(u,v,w);
         f[i]=w;
     }
     sort(f+,f++m);
     printf("%d\n",bsearch(,m));
     return ;
 }

Spfa:

 #include <bits/stdc++.h>
 using namespace std;

 const int maxn=+,maxm=+,INF=<<;
 int n,m,k,ect;
 int hd[maxn],q[maxn],f[maxm],d[maxn];
 bool vis[maxn];
 struct edge{
     int to,w,next;
     edge(int to=,int w=,int next=):to(to),w(w),next(next){}
 }g[maxm<<];
 inline int read(int &x){ x=;int k=;char c;for(c=getchar();c<''||c>'';c=getchar())if(c=='-')k=-;for(;c>=''&&c<='';c=getchar())x=x*+c-'';return x*=k; }
 inline void add_edge(int u,int v,int w){
     g[++ect]=edge(v,w,hd[u]); hd[u]=ect;
     g[++ect]=edge(u,w,hd[v]); hd[v]=ect;
 }
 inline bool C(int x){
     for(int i=;i<=n;i++) d[i]=INF, vis[i]=false;
     d[]=,vis[]=true;
     int l=,r=;
     q[r++]=;
     while(l!=r){
         int u=q[l++]; if(l==maxn-) l=;
         vis[u]=false;
         for(int i=hd[u];i;i=g[i].next){
             int v=g[i].to,duv=g[i].w>x?:;
             if(d[v]>d[u]+duv){
                 d[v]=d[u]+duv;
                 if(!vis[v]){
                     q[r++]=v; if(r==maxn-) r=;
                     vis[v]=true;
                 }
             }
         }
     }
     return d[n]<=k;
 }
 inline int bsearch(int l,int r){
     if(!C(f[r])) return-;
     while(l<r){
         int mid=l+(r-l)/;
         if(C(f[mid])) r=mid;
         else l=mid+;
     }
     return f[l];
 }
 int main(){
     read(n); read(m); read(k);
     for(int i=,u,v,w;i<=m;i++){
         read(u); read(v); read(w);
         add_edge(u,v,w);
         f[i]=w;
     }
     sort(f+,f++m);
     printf("%d\n",bsearch(,m));
     return ;
 }