LCA最近公共祖先模板代码

vector模拟邻接表：

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #include<vector>
 6 #include<queue>
 7 #define eps 1e-8
 8 #define memset(a,v) memset(a,v,sizeof(a))
 9 using namespace std;
10 typedef long long int LL;
11 const int MAXL(1e4);
12 const int INF(0x7f7f7f7f);
13 const int mod(1e9+7);
14 int dir[4][2]= {{-1,0},{1,0},{0,1},{0,-1}};
15 int father[MAXL+50];
16 bool is_root[MAXL+50];
17 bool vis[MAXL+50];
18 vector<int>v[MAXL+50];
19 int root;
20 int cx,cy;
21 int ans;
22 int Find(int x)
23 {
24     if(x!=father[x])
25         father[x]=Find(father[x]);
26     return father[x];
27 }
28  
29 void Join(int x,int y)
30 {
31     int fx=Find(x),fy=Find(y);
32     if(fx!=fy)
33         father[fy]=fx;
34 }
35  
36 void LCA(int u)
37 {
38     for(int i=0; i<v[u].size(); i++)
39     {
40         int child=v[u][i];
41         if(!vis[child])
42         {
43             LCA(child);
44             Join(u,child);
45             vis[child]=true;
46         }
47     }
48     if(u==cx&&vis[cy]==true)
49         ans=Find(cy);
50     if(u==cy&&vis[cx]==true)
51         ans=Find(cx);
52  
53 }
54  
55 void init()
56 {
57     memset(is_root,true);
58     memset(vis,false);
59     int n;
60     scanf("%d",&n);
61     for(int i=0; i<=n; i++)
62         v[i].clear();
63     for(int i=1; i<=n; i++)
64         father[i]=i;
65     for(int i=1; i<n; i++)
66     {
67         int x,y;
68         scanf("%d%d",&x,&y);
69         v[x].push_back(y);
70         is_root[y]=false;
71     }
72     scanf("%d%d",&cx,&cy);
73     for(int i=1; i<=n; i++)
74     {
75         if(is_root[i]==true)
76         {
77             root=i;
78             break;
79         }
80     }
81  
82 }
83 int main()
84 {
85     int T;
86     scanf("%d",&T);
87     while(T--)
88     {
89         init();
90         LCA(root);
91         cout<<ans<<endl;
92     }
93 }
94  

链式前向星写法：

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<cmath>
  5 #include<vector>
  6 #include<queue>
  7 #define eps 1e-8
  8 #define memset(a,v) memset(a,v,sizeof(a))
  9 using namespace std;
 10 typedef long long int LL;
 11 const int MAXL(1e6);
 12 const int INF(0x7f7f7f7f);
 13 const int mod(1e9+7);
 14 int dir[4][2]= {{-1,0},{1,0},{0,1},{0,-1}};
 15 struct node
 16 {
 17     int to;
 18     int next;
 19 }edge[MAXL+50];
 20 int head[MAXL+50];
 21 int father[MAXL+50];
 22 bool vis[MAXL+50];
 23 bool is_root[MAXL+50];
 24 int n;
 25 int cnt;
 26 int cx,cy;
 27 int ans;
 28 int root;
 29  
 30  
 31 int Find(int x)
 32 {
 33     if(x!=father[x])
 34         father[x]=Find(father[x]);
 35     return father[x];
 36 }
 37  
 38 void Join(int x,int y)
 39 {
 40     int fx=Find(x),fy=Find(y);
 41     if(fx!=fy)
 42         father[fy]=fx;
 43 }
 44  
 45 void add_edge(int x,int y)
 46 {
 47     edge[cnt].to=y;
 48     edge[cnt].next=head[x];
 49     head[x]=cnt++;
 50 }
 51  
 52 void init()
 53 {
 54     cnt=0;
 55     memset(head,-1);
 56     memset(vis,false);
 57     memset(is_root,true);
 58     scanf("%d",&n);
 59     for(int i=0;i<=n;i++)
 60         father[i]=i;
 61     for(int i=1;i<n;i++)
 62     {
 63         int x,y;
 64         scanf("%d%d",&x,&y);
 65         add_edge(x,y);
 66         is_root[y]=false;
 67     }
 68     for(int i=1;i<=n;i++)
 69         if(is_root[i]==true)
 70             root=i;
 71 }
 72  
 73 void LCA(int u)
 74 {
 75     for(int i=head[u];~i;i=edge[i].next)
 76     {
 77         int v=edge[i].to;
 78         LCA(v);
 79         Join(u,v);
 80         vis[v]=true;
 81  
 82     }
 83     if(cx==u&&vis[cy]==true)
 84         ans=Find(cy);
 85     if(cy==u&&vis[cx]==true)
 86         ans=Find(cx);
 87 }
 88 void solve()
 89 {
 90     scanf("%d%d",&cx,&cy);
 91     LCA(root);
 92 }
 93 int main()
 94 {
 95     int T;
 96     scanf("%d",&T);
 97     while(T--)
 98     {
 99         init();
100         solve();
101         cout<<ans<<endl;
102     }
103 }
104  

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

来源：https://www.cnblogs.com/baiyi-destroyer/p/9415278.html