LCA 倍增算法模板

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 #include <cstring>
 #include <cstdio>
 #include <cstdlib>
 #include <algorithm>
 #include <cmath>
 #include <vector>
 using namespace std;
 const int N=+;
 vector <int> son[N];
 int T,n,depth[N],fa[N][],in[N],a,b;
 void dfs(int prev,int rt){
     depth[rt]=depth[prev]+;
     fa[rt][]=prev;
     for (int i=;i<;i++)
         fa[rt][i]=fa[fa[rt][i-]][i-];
     for (int i=;i<son[rt].size();i++)
         dfs(rt,son[rt][i]);
 }
 int LCA(int x,int y){
     if (depth[x]<depth[y])
         swap(x,y);
     for (int i=;i>=;i--)
         if (depth[x]-(<<i)>=depth[y])
             x=fa[x][i];
     if (x==y)
         return x;
     for (int i=;i>=;i--)
         if (fa[x][i]!=fa[y][i])
             x=fa[x][i],y=fa[y][i];
     return fa[x][];
 }
 int main(){
     scanf("%d",&T);
     while (T--){
         scanf("%d",&n);
         for (int i=;i<=n;i++)
             son[i].clear();
         memset(in,,sizeof in);
         for (int i=;i<n;i++){
             scanf("%d%d",&a,&b);
             son[a].push_back(b);
             in[b]++;
         }
         depth[]=-;
         int rt=;
         for (int i=;i<=n&&rt==;i++)
             if (in[i]==)
                 rt=i;
         dfs(,rt);
         scanf("%d%d",&a,&b);
         printf("%d\n",LCA(a,b));
     }
     return ;
 }