LCA template tree section seeking

•  O（logn）（n<=10^6）
• https://www.cnblogs.com/cangT-Tlan/p/8846408.html
• The tree is divided into a chain of several, to maintain a data structure of each chain

•  1 #include<bits/stdc++.h>
   2 #define ll long long
   3 #define rll register ll
   4 #define M 0x3f3f3f
   5 #define For(i,l,r) for(int i=l;i<=r;i++)
   6 using namespace std; 
   7 ll n,m,s,head[M],a[M],x,y,z,tot,k,t;
   8 ll fa[M],d[M],top[M],size[M],id[M],ril[M];
   9 struct node1{
  10     ll to,nxt;
  11 }e[M<<1];
  12 struct node2{
  13     ll l,r,sum,flag;
  14 }tree[M<<1];
  15 
  16 inline ll read(){
  17     ll f=1,sum=0;
  18     char ch=getchar();
  19     while(!isdigit(ch)){if(ch=='-')f=-1;ch=getchar();}
  20     while(isdigit(ch)){sum=(sum<<1)+(sum<<3)+(ch^48);ch=getchar();}
  21     return f*sum;
  22 }
  23 
  24 inline void add(ll x,ll y){
  25      E [++ TOT] .to = Y;
   26 is      E [TOT] = .nxt head [X];
   27      head [X] = TOT;
   28  }
   29  
  30 inline void DFS1 (U LL) { // first pass dfs tree traversal, the depth d pretreatment, size this point node number, FA parent node 
  31 is      d [U] = d [FA [U]] + . 1 ;
   32      size [U] = . 1 ;
   33 is      for (RLL = I head [U]; I; I = E [I] .nxt) {
   34 is          IF (E [I] .to =! FA [U]) {
   35              FA [E [I] .to] = U;
   36              DFS1 ( E [I] .to);
   37 [              size [U] + =size [E [I] .to];
   38 is          }
   39      }
   40  }
   41 is  
  42 is inline void DFS2 (U LL) { // according to the severity of the number of child nodes edge division number, ensure that only a point in a chain. Usually only the heavy side and light side less than. 
  43 is      LL T = 0 ; // Top i.e. the point where the heavy edges for this vertex 
  44 is      IF Top [U] = (Top [U]!) U;
   45      for (RLL head I = [U]; I; I = E [I] .nxt) {
   46 is          IF (E [I] .to FA = [U] && size [E [I] .to]> T) T =! E [I] .to;
   47      }
   48      IF (T) {
   49          Top [T] = Top [U];
   50          DFS2 (T);
  51 is      }
   52 is      for (RLL head I = [U]; I; I = E [I] .nxt) {
   53 is          IF (E [I] .to FA = [U] && E [I] .to =!! T) DFS2 (E [I] .to); 
   54 is      }
   55  }
   56 is  
  57 is inline LCA LL (LL X, Y LL) { // when the two points are located on a heavy chain that is the same operation is ended. Otherwise, skip to the depth where the depth of the point of the heavy chain of a point, the position of the point of the shallow depth at the end of the operation is also desired LCA 
  58      the while (Top [X]! = Top [Y]) {
   59          IF (D [Top [X]] < D [Top [Y]]) the swap (X, Y);
   60          X = FA [Top [X]];
   61 is      }
   62 is      IF (D [X]> D [Y]) the swap (X, Y);
   63 is      return X;
   64 }
  65 
  66 int main(){
  67     n=read(),m=read(),s=read();
  68     For(i,1,n-1) {x=read(),y=read(),add(x,y),add(y,x);}
  69     dfs1(s),dfs2(s);
  70     For(i,1,m){x=read(),y=read(),printf("%lld\n",lca(x,y));}
  71     return 0;
  72 }