货车运输 vijos 1843 NOIP2013 D1T3 最大生成树，并查集，（伪·LCA）

  1 #include<cstdio>
  2 #include<cstring>
  3 #include<algorithm>
  4 #include<cmath>
  5 #include<iostream>
  6 using namespace std;
  7 template<class T> inline void read(T &_a){
  8     bool f=0;int _ch=getchar();_a=0;
  9     while(_ch<‘0‘ || _ch>‘9‘){if(_ch==‘-‘)f=1;_ch=getchar();}
 10     while(_ch>=‘0‘ && _ch<=‘9‘){_a=(_a<<1)+(_a<<3)+_ch-‘0‘;_ch=getchar();}
 11     if(f)_a=-_a;
 12 }
 13 
 14 const int maxn=10001,maxm=50001;
 15 int n,m,egcnt,head[maxn],Q,egcnttt,belong[maxn],fa[maxn],tmp[maxn];
 16 bool vis[maxn];
 17 struct edge {int to,next,dis;}w[maxn<<1];
 18 struct edge2{
 19     int from,to,dis;
 20     inline bool operator < (const edge2 x) const {return dis>x.dis;}
 21 }edg[maxm];
 22 
 23 inline void addedge2(int from,int to,int dis)
 24 {
 25     edg[++egcnttt].to=to;
 26     edg[egcnttt].from=from;
 27     edg[egcnttt].dis=dis;
 28 }
 29 
 30 inline void addedge(int from,int to,int dis)
 31 {
 32     w[++egcnt].to=to;
 33     w[egcnt].next=head[from];
 34     w[egcnt].dis=dis;
 35     head[from]=egcnt;
 36     w[++egcnt].to=from;
 37     w[egcnt].next=head[to];
 38     w[egcnt].dis=dis;
 39     head[to]=egcnt;
 40 }
 41 
 42 int find(int u)
 43 { return belong[u]==u?u:belong[u]=find(belong[u]); }
 44 
 45 inline void kruskal()
 46 {
 47     sort(edg+1,edg+egcnttt+1);
 48     for (register int i=1;i<=n;++i) belong[i]=i;
 49     for (register int i=1;i<=egcnttt&&egcnt<((n-1)<<1);++i)
 50     {
 51         int a1=find(edg[i].from);
 52         int a2=find(edg[i].to);
 53         if(a1!=a2)
 54         {
 55             belong[a1]=a2;
 56             addedge(edg[i].from,edg[i].to,edg[i].dis);
 57         }
 58     }
 59 }
 60 
 61 void dfs_fa(int u)
 62 {
 63     for (register int i=head[u];i;i=w[i].next)
 64         if(!fa[w[i].to]) fa[w[i].to]=u,dfs_fa(w[i].to);
 65 }
 66 
 67 inline int solve(int x,int y)
 68 {
 69     if(!fa[x]) fa[x]=-1,dfs_fa(x);
 70     memset(tmp,0x7f,sizeof(tmp));
 71     tmp[x]=10000000;
 72     while(x!=-1)
 73     {
 74         for (register int i=head[x];i;i=w[i].next)
 75         if(w[i].to==fa[x])
 76         {
 77             tmp[w[i].to]=min(w[i].dis,tmp[x]);
 78             break;
 79         }
 80         x=fa[x];
 81     }
 82     int ans=10000000;
 83     while(y!=-1)
 84     {
 85         if(tmp[y]<=10000000) {ans=min(ans,tmp[y]); break;}
 86         for (register int i=head[y];i;i=w[i].next)
 87         if(w[i].to==fa[y])
 88         {
 89             ans=min(w[i].dis,ans);
 90             break;
 91         }
 92         y=fa[y];
 93     }
 94     return ans;
 95 }
 96 
 97 int main()
 98 {
 99     read(n); read(m);
100     for (register int i=1,x,y,z;i<=m;++i) read(x),read(y),read(z),addedge2(x,y,z);
101     kruskal();
102     for (read(Q);Q;--Q)
103     {
104         int x,y;
105         read(x); read(y);
106         int a1=find(x);
107         int a2=find(y);
108         if(a1!=a2) {printf("-1\n"); continue;}
109         printf("%d\n",solve(x,y));
110     }
111     return 0;
112 }