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

posted @ 2019-03-04 13:24  AlenaNuna  阅读(126)  评论(0编辑  收藏  举报