2017暑期集训Day 8

 1 #include<iostream> 
 2 #include<cmath> 
 3 #include<cstdio> 
 4 #include<cstdlib> 
 5 #include<cstring> 
 6 #include<vector> 
 7 #include<queue> 
 8 #include<algorithm> 
 9 using namespace std; 
10 vector<int>g[500005]; 
11 queue<int>q; 
12 const int maxpow=30; 
13 int fa[40][500005]={0},dep[500005]={0}; 
14 int n,p,rt,x,y; 
15 bool vis[500005]={0}; 
16 void bfs(int u) 
17 { 
18     vis[u]=true;q.push(u); 
19     while(!q.empty()) 
20     { 
21         u=q.front(); 
22         for (int i=0;i<g[u].size();i++) 
23         { 
24             int v=g[u][i]; 
25             if (!vis[v]){dep[v]=dep[u]+1;q.push(v);} 
26         } 
27         q.pop(); 
28     } 
29 } 
30 void dup() 
31 { 
32     for (int j=1;j<=maxpow;j++) 
33     for (int i=1;i<=n;i++) 
34     fa[j][i]=fa[j-1][fa[j-1][i]]; 
35 } 
36 int lca(int u,int v) 
37 { 
38     if (dep[u]<dep[v]) swap(u,v); 
39     int dif=dep[u]-dep[v]; 
40     for (int i=0;i<maxpow;i++) if ((1<<i)&dif) u=fa[i][u]; 
41     if (u==v) return u; 
42     for (int i=maxpow-1;i>=0;i--) 
43     if (fa[i][u]!=fa[i][v]) {u=fa[i][u];v=fa[i][v];} 
44     u=fa[0][u];return u;     
45 } 
46 int main() 
47 { 
48     scanf("%d%d",&n,&p); 
49     for(int i=1;i<=n;i++) g[i].clear(); 
50     for(int i=1;i<n;i++) 
51     { 
52         scanf("%d%d",&x,&y);g[x].push_back(y);fa[0][y]=x; 
53         if (!fa[0][x]) rt=x; 
54     } 
55     dep[rt]=1;bfs(rt);dup(); 
56     for (int k=1;k<=p;k++) 
57     { 
58         scanf("%d%d",&x,&y); 
59         printf("%d\n",lca(x,y)); 
60     } 
61     return 0; 
62 }

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #define Mx 500005
 5 using namespace std; 
 6 struct edge{int to,next;}e[1500005]; 
 7 int h[Mx],q[Mx],f[Mx],a[Mx],cnt=0,n,m,c,b; 
 8 bool r[Mx]; 
 9 inline void ins(int *h,int x,int y){e[++cnt].to=y;e[cnt].next=h[x];h[x]=cnt;} 
10 inline int ff(int x){return f[x]?f[x]=ff(f[x]):x;} 
11 int tarjan(int u){ 
12     for (int i=h[u];i;i=e[i].next){tarjan(e[i].to);f[e[i].to]=u;} 
13     for (int i=q[u];i;i=e[i].next) 
14     if(a[e[i].to]) a[e[i].to]=ff(a[e[i].to]); 
15     else a[e[i].to]=u; 
16       
17 } 
18 int main() 
19 { 
20     scanf("%d%d",&n,&m); 
21     for(int i=1;i<n;i++){scanf("%d%d",&c,&b);ins(h,c,b);r[b]=1;} 
22     for(int i=0;i<m;i++){scanf("%d%d",&c,&b);ins(q,c,i);ins(q,b,i);} 
23     for(int i=1;i<=n;i++)if(!r[i]){tarjan(i);break;} 
24     for(int i=0;i<m;i++)printf("%d\n",a[i]); 
25     return 0; 
26 }