Hdu 2874 (LCA)

During the virtual competition, the shortest was to find the shortest path of any two points. No matter how the optimization was done, it timed out. Recently, some tree questions were made. This is the distance from any two points to the nearest common ancestor, first, determine whether China Unicom is connected with the nearest public ancestor by using the Union and difference set. First, construct the image into a pair of tokens,

 

 

 

 

 

#include<string.h>#include<stdio.h>#define N 10010int father[N],dfs[N],n,vis[N],head[N],num,f[N],ans,dis[N];struct edge{int st,ed,next,w;}E[N*2];void addedge(int x,int y,int w){E[num].st=x;E[num].ed=y;E[num].w=w;E[num].next=head[x];head[x]=num++;}int find(int a){if(f[a]!=a)f[a]=find(f[a]);return f[a];}void dfs1(int u){int i,v;vis[u]=1;for(i=head[u];i!=-1;i=E[i].next){v=E[i].ed;if(vis[v]==1)continue;father[v]=u;dfs[v]=dfs[u]+1;dis[v]=E[i].w;dfs1(v);}if(ans<dfs[u])ans=dfs[u];}int LCA(int x,int y){int sum=0;while(dfs[x]>dfs[y]){sum+=dis[x];x=father[x];}while(dfs[y]>dfs[x]){sum+=dis[y];y=father[y];}while(x!=y){sum+=(dis[x]+dis[y]);x=father[x];y=father[y];}return sum;}int main(){int i,j,k,x,y,m,ans,w;while(scanf("%d%d%d",&n,&m,&k)!=-1){memset(head,-1,sizeof(head));num=0;for(i=1;i<=n;i++)f[i]=i;for(i=0;i<m;i++){scanf("%d%d%d",&x,&y,&w);addedge(x,y,w);addedge(y,x,w);x=find(x);y=find(y);if(x!=y)f[x]=find(y);}memset(vis,0,sizeof(vis));ans=1;for(i=1;i<=n;i++){if(vis[i]==0){dis[i]=0;dfs[i]=ans;father[i]=i;dfs1(i);ans++;}}while(k--){scanf("%d%d",&x,&y);if(find(x)!=find(y)){printf("Not connected\n");continue;}j=LCA(x,y);printf("%d\n",j);}}return 0;}