Description

Input

Output

Sample Input

Sample Output

HINT

Source

Day1

如圖：這是一般的情況如果選取a點為集合點的話將會有兩個人x,y走ab這條路徑，但是如果選取b點為集合點的話只有一個人z走ab這條路徑，hzwer的兩個lca相同的情況就相當於是告訴你了a是x,y的祖先的祖先

 1 #include "bits/stdc++.h"
 2 using namespace std;
 3 typedef long long LL;
 4 const int MAX=5e5+5;
 5 int n,m;
 6 int tot,head[MAX],adj[MAX<<1
 
],next[MAX<<1];
 7 int fa[MAX][21],deep[MAX];
 8 bool vis[MAX];
 9 inline int read(){
10     int an=0,x=1;char c=getchar();
11     while (c<‘0‘ || c>‘9‘) {if (c==‘-‘) x=-1;c=getchar();}
12     while (c>=‘0‘ && c<=‘9‘) {an=(an<<3)+(an<<1)+c-‘0‘;c=getchar();}
13     return
 
 an;
14 }
15 void addedge(int u,int v){
16     tot++,adj[tot]=v,next[tot]=head[u],head[u]=tot;
17 }
18 void dfs(int x){
19     vis[x]=true;
20     int i,j;
21     for (i=1;i<=20;i++){
22         if (deep[x]<(1<<i)) break;
23         fa[x][i]=fa[fa[x][i-1]][i-1];
24     }
25     for (i=head[x];i;i=next[i]){
26         if (!vis[adj[i]]){
27             deep[adj[i]]=deep[x]+1;
28             fa[adj[i]][0]=x;
29             dfs(adj[i]);
30         }
31     }
32 }
33 int lca(int x,int y){
34     int i,j;
35     if (deep[x]<deep[y]) swap(x,y);
36     int dd=deep[x]-deep[y];
37     for (i=20;i>=0;i--)
38         if (dd&(1<<i)) x=fa[x][i];
39     for (i=20;i>=0;i--)
40         if (fa[x][i]!=fa[y][i]){
41             x=fa[x][i],y=fa[y][i];
42         }
43     return x==y?x:fa[x][0];
44 }
45 inline int dist(int x,int y,int z){return deep[x]+deep[y]-2*deep[z];}
46 int main(){
47     freopen ("emer.in","r",stdin);freopen ("emer.out","w",stdout);
48     int i,j,u,v,x,y,z,xy,yz,zx,dis;
49     n=read(),m=read();
50     for (i=1;i<n;i++){
51         u=read(),v=read();
52         addedge(u,v),addedge(v,u);
53     }
54     dfs(1);
55     for (i=1;i<=m;i++){
56         x=read(),y=read(),z=read();
57         dis=0;
58         xy=lca(x,y),zx=lca(x,z),yz=lca(y,z);
59         if (xy==zx){
60             printf("%d ",yz);
61             dis=dist(y,yz,yz)+dist(z,yz,yz)+dist(yz,x,xy);
62             printf("%d\n",dis);
63         }
64         else if (xy==yz){
65             printf("%d ",zx);
66             dis=dist(zx,x,zx)+dist(z,zx,zx)+dist(zx,y,xy);
67             printf("%d\n",dis);
68         }
69         else if (zx==yz){
70             printf("%d ",xy);
71             dis=dist(xy,x,xy)+dist(y,xy,xy)+dist(xy,z,zx);
72             printf("%d\n",dis);
73         }
74     }
75     return 0;
76 }

BZOJ-1787: [Ahoi2008]Meet 緊急集合 (LCA)