[树上倍增] BZOJ 4281 [ONTAK2015]Związek Harcerstwa Bajtockiego

树上倍增裸题

%%%用树链剖分拿rank3的Evan大爷

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
#define V G[p].v
using namespace std;

inline char nc()
{
	static char buf[100000],*p1=buf,*p2=buf;
	if (p1==p2) { p2=(p1=buf)+fread(buf,1,100000,stdin); if (p1==p2) return EOF; }
	return *p1++;
}

inline void read(int &x){
	char c=nc(),b=1;
	for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;
	for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;
}

struct edge{
	int u,v;
	int next;
};

edge G[2000005];
int head[1000005],inum;

inline void add(int u,int v,int p){
	G[p].u=u; G[p].v=v; G[p].next=head[u]; head[u]=p;
}

int n,depth[1000005];
int fat[1000005][25];

inline void dfs(int u,int fa){
	fat[u][0]=fa; depth[u]=depth[fa]+1;
	for (int p=head[u];p;p=G[p].next)
		if (V!=fa)
			dfs(V,u);
}

inline int Dis(int x,int y){
	return depth[y]-depth[x];
}

inline int LCA(int u,int v){
	if (depth[u]<depth[v]) swap(u,v);
	for (int k=22;~k;k--)
		if ((depth[u]-depth[v])&(1<<k))
			u=fat[u][k];
	if (u==v) return v;
	for (int k=22;~k;k--)
		if (fat[u][k]!=fat[v][k])
			u=fat[u][k],v=fat[v][k];
	return fat[u][0];
}

inline int Fat(int u,int d){
	for (int k=22;~k;k--)
		if (d&(1<<k))
			u=fat[u][k];
	return u;
}

int main()
{
	int iu,iv,K;
	int s,t,len;
	freopen("t.in","r",stdin);
	freopen("t.out","w",stdout);
	read(n); read(s); read(K);
	for (int i=1;i<n;i++)
		read(iu),read(iv),add(iu,iv,++inum),add(iv,iu,++inum);
	dfs(1,0);
	for (int k=1;k<=22;k++)
		for (int i=1;i<=n;i++)
			fat[i][k]=fat[fat[i][k-1]][k-1];
	while (K--)
	{
		read(t); read(len);
		int lca=LCA(s,t);
		if (Dis(lca,s)+Dis(lca,t)<=len)
			s=t;
		else if (Dis(lca,s)>=len)
			s=Fat(s,len);
		else if (Dis(lca,s)+Dis(lca,t)>=len)
			s=Fat(t,Dis(lca,s)+Dis(lca,t)-len);
		printf("%d ",s);
	}
	return 0;
}