LCA || BZOJ 1602: [Usaco2008 Oct]牧场行走 || Luogu P2912 [USACO08OCT]牧场散步Pasture Walking
题面：[USACO08OCT]牧场散步Pasture Walking
题解：LCA模版题
代码：
1 #include<cstdio> 2 #include<cstring> 3 #include<iostream> 4 using namespace std; 5 const int maxn=1000,max_log=10; 6 int N,Q,F[maxn+5][max_log+2],edge_head[maxn+5],num_edge=0,c,Dep[maxn+5],u,v,w,A,B; 7 int Sig[maxn+5]; 8 struct Edge{ 9 int to,nx,dis; 10 }edge[(maxn<<1)+5]; 11 inline void Add_edge(int from,int to,int dis){ 12 edge[++num_edge].nx=edge_head[from]; 13 edge[num_edge].to=to; 14 edge[num_edge].dis=dis; 15 edge_head[from]=num_edge; 16 return; 17 } 18 inline void Dfs(int x,int fa){ 19 Dep[x]=Dep[fa]+1; 20 F[x][0]=fa; 21 for(int i=1;i<=max_log;i++) 22 F[x][i]=F[F[x][i-1]][i-1]; 23 for(int i=edge_head[x];i;i=edge[i].nx){ 24 int y=edge[i].to; 25 if(y==fa)continue; 26 Sig[y]=Sig[x]+edge[i].dis; 27 Dfs(y,x); 28 } 29 return; 30 } 31 inline int LCA(int x,int y){ 32 if(Dep[x]<Dep[y]){ 33 int t=x;x=y;y=t; 34 } 35 for(int i=max_log;i>=0;i--){ 36 int a;a=F[x][i]; 37 if(Dep[a]>=Dep[y])x=a; 38 if(x==y)return x; 39 } 40 for(int i=max_log;i>=0;i--){ 41 int a,b;a=F[x][i];b=F[y][i]; 42 if(a!=b){ 43 x=a;y=b; 44 } 45 } 46 return F[x][0]; 47 } 48 int main(){ 49 scanf("%d%d",&N,&Q); 50 for(int i=1;i<N;i++){ 51 scanf("%d%d%d",&u,&v,&w); 52 Add_edge(u,v,w); 53 Add_edge(v,u,w); 54 } 55 Dfs(1,0); 56 while(Q--){ 57 scanf("%d%d",&A,&B); 58 c=LCA(A,B); 59 printf("%d\n",Sig[A]+Sig[B]-Sig[c]-Sig[c]); 60 } 61 return 0; 62 }
By:AlenaNuna
