LCA Tarjan

初二学完忘了QAQ,今天再学一发

原题Link:https://www.luogu.org/problem/show?pid=3379

Code:

 1 #include <iostream>
 2 #include <cstdio>
 3 const int maxn=500000*2+100;
 4 int n,m,i,to[maxn],root,x,y,last[maxn],next[maxn],next1[maxn],last1[maxn],to1[maxn],ans[maxn],fa[maxn],v[maxn];
 5 using namespace std;
 6 inline void read(int &k)
 7 {
 8     int f=1;char c=getchar();k=0;
 9     while (c<'0'||c>'9')c=='-'&&(f=-1),c=getchar();
10     while (c>='0'&&c<='9')k=k*10+c-'0',c=getchar();
11     k*=f;
12 }
13 inline int gf(int now)
14 {
15     return fa[now]==now?now:fa[now]=gf(fa[now]);
16 }
17 inline void dfs(int now)
18 {
19     v[now]=1;
20     for(int cur=last[now];cur;cur=next[cur])
21     {
22         if (!v[to[cur]])
23         {
24             dfs(to[cur]);
25             fa[to[cur]]=now;
26         }
27     }
28     for (int cur=last1[now];cur;cur=next1[cur])
29     if (v[to1[cur]])ans[(cur+1)>>1]=gf(to1[cur]);
30 }
31 int main()
32 {
33     read(n);read(m);read(root);
34     for (i=1;i<n;i++)
35     {
36         read(x);read(y);
37         to[i*2-1]=y;
38         next[i*2-1]=last[x];
39         last[x]=i*2-1;
40         to[i*2]=x;
41         next[i*2]=last[y];
42         last[y]=i*2;
43     }
44     for (i=1;i<=m;i++)
45     {
46         read(x);read(y);
47         to1[i*2-1]=y;
48         next1[i*2-1]=last1[x];
49         last1[x]=i*2-1;
50         to1[i*2]=x;
51         next1[i*2]=last1[y];
52         last1[y]=i*2;
53     }
54     for (i=1;i<=n;i++)fa[i]=i;
55     dfs(root);
56     for (i=1;i<=m;i++)
57     printf("%d\n",ans[i]);
58 }
View Code

 

posted @ 2017-08-10 16:29  Michael_Zhuang  阅读(96)  评论(0编辑  收藏  举报