题号：洛谷3379
1 %:pragma GCC optimize ("Ofast") 2 #include<cstdio> 3 #include<vector> 4 #include<cctype> 5 inline int getint() { 6 int ch; 7 while(!isdigit(ch=getchar())); 8 int x=ch^'0'; 9 while(isdigit(ch=getchar())) x=(((x<<2)+x)<<1)+(ch^'0'); 10 return x; 11 } 12 const int N=500001,logN=19; 13 std::vector<int> e[N]; 14 int anc[N][logN+1]={{0}},dep[N]; 15 inline void add_edge(const int u,const int v) { 16 e[u].push_back(v); 17 e[v].push_back(u); 18 } 19 void dfs(const int x,const int parent,const int depth) { 20 anc[x][0]=parent,dep[x]=depth; 21 for(int i=1;i<=logN;i++) { 22 anc[x][i]=anc[anc[x][i-1]][i-1]; 23 } 24 for(unsigned int i=0;i<e[x].size();i++) { 25 if(e[x][i]==parent) continue; 26 dfs(e[x][i],x,depth+1); 27 } 28 } 29 inline void swap(int &a,int &b) { 30 int t; 31 t=a; 32 a=b; 33 b=t; 34 } 35 int LCA(int a,int b) { 36 if(dep[a]<dep[b]) swap(a,b); 37 for(int i=logN;i>=0;i--) { 38 if(dep[a]-(1<<i)>=dep[b]) a=anc[a][i]; 39 } 40 if(a==b) return a; 41 for(int i=logN;i>=0;i--) { 42 if(anc[a][i]&&anc[a][i]!=anc[b][i]) { 43 a=anc[a][i]; 44 b=anc[b][i]; 45 } 46 } 47 return anc[a][0]; 48 } 49 int main() { 50 int n=getint(),m=getint(),s=getint(); 51 for(int i=1;i<n;i++) add_edge(getint(),getint()); 52 dfs(s,0,0); 53 while(m--) printf("%d ",LCA(getint(),getint())); 54 return 0; 55 }