LCA最近公共祖先模板代码

vector模拟邻接表：

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<vector>
 #include<queue>
 #define eps 1e-8
 #define memset(a,v) memset(a,v,sizeof(a))
 using namespace std;
 typedef long long int LL;
 const int MAXL(1e4);
 const int INF(0x7f7f7f7f);
 const int mod(1e9+);
 int dir[][]= {{-,},{,},{,},{,-}};
 int father[MAXL+];
 bool is_root[MAXL+];
 bool vis[MAXL+];
 vector<int>v[MAXL+];
 int root;
 int cx,cy;
 int ans;
 int Find(int x)
 {
     if(x!=father[x])
         father[x]=Find(father[x]);
     return father[x];
 }

 void Join(int x,int y)
 {
     int fx=Find(x),fy=Find(y);
     if(fx!=fy)
         father[fy]=fx;
 }

 void LCA(int u)
 {
     for(int i=; i<v[u].size(); i++)
     {
         int child=v[u][i];
         if(!vis[child])
         {
             LCA(child);
             Join(u,child);
             vis[child]=true;
         }
     }
     if(u==cx&&vis[cy]==true)
         ans=Find(cy);
     if(u==cy&&vis[cx]==true)
         ans=Find(cx);

 }

 void init()
 {
     memset(is_root,true);
     memset(vis,false);
     int n;
     scanf("%d",&n);
     for(int i=; i<=n; i++)
         v[i].clear();
     for(int i=; i<=n; i++)
         father[i]=i;
     for(int i=; i<n; i++)
     {
         int x,y;
         scanf("%d%d",&x,&y);
         v[x].push_back(y);
         is_root[y]=false;
     }
     scanf("%d%d",&cx,&cy);
     for(int i=; i<=n; i++)
     {
         if(is_root[i]==true)
         {
             root=i;
             break;
         }
     }

 }
 int main()
 {
     int T;
     scanf("%d",&T);
     while(T--)
     {
         init();
         LCA(root);
         cout<<ans<<endl;
     }
 }
  

链式前向星写法：

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<vector>
 #include<queue>
 #define eps 1e-8
 #define memset(a,v) memset(a,v,sizeof(a))
 using namespace std;
 typedef long long int LL;
 const int MAXL(1e6);
 const int INF(0x7f7f7f7f);
 const int mod(1e9+);
 int dir[][]= {{-,},{,},{,},{,-}};
 struct node
 {
     int to;
     int next;
 }edge[MAXL+];
 int head[MAXL+];
 int father[MAXL+];
 bool vis[MAXL+];
 bool is_root[MAXL+];
 int n;
 int cnt;
 int cx,cy;
 int ans;
 int root;

 int Find(int x)
 {
     if(x!=father[x])
         father[x]=Find(father[x]);
     return father[x];
 }

 void Join(int x,int y)
 {
     int fx=Find(x),fy=Find(y);
     if(fx!=fy)
         father[fy]=fx;
 }

 void add_edge(int x,int y)
 {
     edge[cnt].to=y;
     edge[cnt].next=head[x];
     head[x]=cnt++;
 }

 void init()
 {
     cnt=;
     memset(head,-);
     memset(vis,false);
     memset(is_root,true);
     scanf("%d",&n);
     for(int i=;i<=n;i++)
         father[i]=i;
     for(int i=;i<n;i++)
     {
         int x,y;
         scanf("%d%d",&x,&y);
         add_edge(x,y);
         is_root[y]=false;
     }
     for(int i=;i<=n;i++)
         if(is_root[i]==true)
             root=i;
 }

 void LCA(int u)
 {
     for(int i=head[u];~i;i=edge[i].next)
     {
         int v=edge[i].to;
         LCA(v);
         Join(u,v);
         vis[v]=true;

     }
     if(cx==u&&vis[cy]==true)
         ans=Find(cy);
     if(cy==u&&vis[cx]==true)
         ans=Find(cx);
 }
 void solve()
 {
     scanf("%d%d",&cx,&cy);
     LCA(root);
 }
 int main()
 {
     int T;
     scanf("%d",&T);
     while(T--)
     {
         init();
         solve();
         cout<<ans<<endl;
     }
 }
  

转自：https://blog.csdn.net/baiyi_destroyer/article/details/81363221