109 lines
2.0 KiB
C++
109 lines
2.0 KiB
C++
#include<cstdio>
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const int maxn=500005;
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const int maxm=50000*2+5;
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struct Rec { int to,lca; Rec *next; };
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Rec edge[maxm],*E[maxn],*ecnt=edge;
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Rec query[maxm],*Q[maxn],*qcnt=query;
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inline void AddEdge(Rec **G,Rec* &ecnt,int from,int to)
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{ ecnt->to=to; ecnt->next=G[from]; G[from]=ecnt++; }
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int n,m,s;
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bool vis[maxn];
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int fa[maxn];
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inline int ff(int x)
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{
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int a=x,b;
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while(x!=fa[x]) x=fa[x];
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while(a!=x)
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{
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b=fa[a];
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fa[a]=x;
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a=b;
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}
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return x;
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}
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void dfs(int u)
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{
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fa[u]=u;
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vis[u]=true;
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for(Rec *it=E[u];it;it=it->next)
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if(!vis[it->to])
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{
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dfs(it->to);
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fa[it->to]=u;
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}
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for(Rec *it=Q[u];it;it=it->next)
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if(vis[it->to])
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{
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it->lca=ff(it->to);
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(query+((it-query)^1))->lca=it->lca;
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}
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}
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int main()
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{
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scanf("%d%d%d",&n,&m,&s);
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for(int i=0;i<n-1;i++)
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{
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int a,b; scanf("%d%d",&a,&b);
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AddEdge(E,ecnt,a,b); AddEdge(E,ecnt,b,a);
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}
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for(int i=0;i<m;i++)
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{
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int a,b; scanf("%d%d",&a,&b);
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AddEdge(Q,qcnt,a,b); AddEdge(Q,qcnt,b,a);
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}
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dfs(s);
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for(int i=0;i<m;i++) printf("%d\n",query[i*2].lca);
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return 0;
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}
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/*
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#include<cstdio>
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#include<vector>
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using namespace std;
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const int maxn=500005;
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struct Node { int v; Node *next; };
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int n,m,s;
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int dep[maxn],anc[maxn][30];
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Node mem[maxn*2],*G[maxn],*ecnt=mem;
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inline void AddEdge(int u,int v) { ecnt->v=v; ecnt->next=G[u]; G[u]=ecnt++; }
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void cal(int o,int fa)
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{
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dep[o]=dep[anc[o][0]]+1;
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for(int i=1;i<=25;i++) anc[o][i]=anc[anc[o][i-1]][i-1];
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for(Node *it=G[o];it;it=it->next)
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if(it->v!=fa)
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{
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anc[it->v][0]=o;
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cal(it->v,o);
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}
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}
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inline int getLCA(int a,int b)
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{
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if(a==b) return a;
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if(dep[b]>dep[a]) swap(a,b);
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for(int i=25;i>=0;i--)
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if(dep[anc[a][i]]>=dep[b]) a=anc[a][i];
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if(a==b) return a;
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for(int i=25;i>=0;i--)
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if(anc[a][i]!=anc[b][i]) a=anc[a][i],b=anc[b][i];
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return anc[a][0];
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}
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int main()
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{
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scanf("%d%d%d",&n,&m,&s);
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for(int i=0;i<n-1;i++)
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{
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int x,y;
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scanf("%d%d",&x,&y);
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AddEdge(x,y); AddEdge(y,x);
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}
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cal(s,0);
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while(m-->0)
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{
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int x,y;
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scanf("%d%d",&x,&y);
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printf("%d\n",getLCA(x,y));
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}
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return 0;
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}
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*/
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