【模板】倍增LCA

题号：洛谷3379

 %:pragma GCC optimize ("Ofast")
 #include<cstdio>
 #include<vector>
 #include<cctype>
 inline int getint() {
     int ch;
     while(!isdigit(ch=getchar()));
     int x=ch^'';
     while(isdigit(ch=getchar())) x=(((x<<)+x)<<)+(ch^'');
     return x;
 }
 const int N=,logN=;
 std::vector<int> e[N];
 int anc[N][logN+]={{}},dep[N];
 inline void add_edge(const int u,const int v) {
     e[u].push_back(v);
     e[v].push_back(u);
 }
 void dfs(const int x,const int parent,const int depth) {
     anc[x][]=parent,dep[x]=depth;
     for(int i=;i<=logN;i++) {
         anc[x][i]=anc[anc[x][i-]][i-];
     }
     for(unsigned int i=;i<e[x].size();i++) {
         if(e[x][i]==parent) continue;
         dfs(e[x][i],x,depth+);
     }
 }
 inline void swap(int &a,int &b) {
     int t;
     t=a;
     a=b;
     b=t;
 }
 int LCA(int a,int b) {
     if(dep[a]<dep[b]) swap(a,b);
     for(int i=logN;i>=;i--) {
         if(dep[a]-(<<i)>=dep[b]) a=anc[a][i];
     }
     if(a==b) return a;
     for(int i=logN;i>=;i--) {
         if(anc[a][i]&&anc[a][i]!=anc[b][i]) {
             a=anc[a][i];
             b=anc[b][i];
         }
     }
     return anc[a][];
 }
 int main() {
     int n=getint(),m=getint(),s=getint();
     for(int i=;i<n;i++) add_edge(getint(),getint());
     dfs(s,,);
     while(m--) printf("%d\n",LCA(getint(),getint()));
     return ;
 }