Hdu 2874 Connections between cities

Test instructions

City Road no ring not necessarily connected tree to find the shortest distance between two cities imagine a lot of little trees.

Ideas:

LCA offline algorithm Then there is a trick that every time we tarjan a tree not the last tree node has visited and the child all-around to find root well, so we just do do do to do it all the city has been visited all the time, you do this little tree will not affect the other trees

#include <cstdio>#include<cstring>#include<algorithm>using namespacestd;intn,m;Const intN =10005;Const intM =1000005;intf[n],next[2*n],va[2*n],wi[2*N],head[n];intVis[n];intnex[2*m],to[2*M],id[m],head[n],ans[m];intFindintx) {    if(X!=f[x]) f[x]=find (f[x]); returnf[x];}intlen,dis[n],l;voidAddintUintVintW) {Va[len]=v; Wi[len]=W; Next[len]=Head[u]; Head[u]=len++;}voidAdd_x (intUintv) {To[l]=v; NEX[L]=Head[u]; Head[u]=l++;} voidLcaintUintFA) {F[u]=T;  for(inti=head[u];i!=-1; i=Next[i]) {intv=va[i],w=Wi[i]; if(v!=FA) {Dis[v]=dis[u]+W;        LCA (V,U); F[V]=u; }} Vis[u]=1;  for(inti=head[u];i!=-1; i=Nex[i]) {        intv=To[i]; if(Vis[v]) {//puts ("SADASD");ans[i/2]=Find (v); }    }    }intMain () {intK;  while(~SCANF ("%d%d%d",&n,&m,&k)) {Len=l=0; memset (Head,-1,sizeofHead); memset (Head,-1,sizeofhead); for(intI=0; i<m;i++)    {            intu,v,w; scanf ("%d%d%d",&u,&v,&W);        Add (U,V,W);    Add (V,U,W); } dis[1]=0;  for(intI=0; i<k;i++)    {        intu,v; scanf ("%d%d",&u,&v); Id[i]=u;        add_x (U,V);    add_x (V,u); }memset (Vis,0,sizeofvis); Memset (F,0,sizeoff); memset (ans,-1,sizeofans);  for(intI=1; i<=n;i++)if(vis[i]==0) LCA (I,0);  for(intI=0; i<l;i+=2)        {                        intA,b,c; A=To[i]; b=id[i/2]; if(Find (a)!=find (b)) puts ("Not connected"); Else{c=ans[i/2]; printf ("%d\n", dis[a]+dis[b]-2*dis[c]);} }    }}

Hdu 2874 Connections between cities