P4949 最短距离(基环树+树链剖分)

题目

P4949 最短距离

做法

先把非树边提出来

查询((x,y))的最短距离就分类查询：树上((x,y))距离，经过非树边距离

带边权查询链长，一个烂大街的套路：树链剖分，节点维护树边距离

待修改随便搞搞就行

Code

#include<bits/stdc++.h>
typedef int LL;
const LL maxn=3e5+9;
inline LL Read(){
	LL x(0),f(1); char c=getchar();
	while(c<'0' || c>'9'){
		if(c=='-') f=-1; c=getchar();
	}
	while(c>='0' && c<='9'){
		x=(x<<3)+(x<<1)+c-'0'; c=getchar();
	}
	return x*f;
}
struct node{
	LL to,nxt,d;
}dis[maxn];
LL num;
LL head[maxn];
inline void Add(LL u,LL v,LL w){
	dis[++num]=(node){v,head[u],w}; head[u]=num;
}
struct E{
	LL u,v,w;
}e[maxn];
LL n,m;
LL n_tree,n_u,n_v,tim,n_d;
LL dep[maxn],size[maxn],visit[maxn],fa[maxn],val[maxn],bel[maxn],son[maxn],dx[maxn],id[maxn],top[maxn];
void Dfs1(LL u,LL f){
	dep[u]=dep[f]+1;
	size[u]=1; visit[u]=true;
	for(LL i=head[u];i;i=dis[i].nxt){
		LL v(dis[i].to); if(v==f) continue;
		if(visit[v]){
			n_tree=i+1>>1; n_u=u; n_v=v; n_d=dis[i].d;
			continue;
		}
		Dfs1(v,u); size[u]+=size[v];
		fa[v]=u; val[v]=dis[i].d; bel[i+1>>1]=v;
		if(size[son[u]]<size[v]) son[u]=v;
	}
}
void Dfs2(LL u,LL up){
	dx[++tim]=u; id[u]=tim;
	top[u]=up;
    if(son[u]) Dfs2(son[u],up);
	for(LL i=head[u];i;i=dis[i].nxt){
		LL v(dis[i].to); if(v==fa[u] || v==son[u] || (i+1>>1)==n_tree) continue;
		Dfs2(v,v);
	}
}
struct Bit{
	LL t[maxn];
	inline LL Lowbit(LL x){
		return x&-x;
	}
	inline void Add(LL x,LL val){
		for(;x<=n;x+=Lowbit(x)) t[x]+=val;
	}
	inline LL Qy(LL x){
		LL ret(0);
		for(;x;x-=Lowbit(x)) ret+=t[x];
		return ret;
	}
	inline LL Query(LL l,LL r){
		return Qy(r)-Qy(l-1);
	}
}Bt;
inline LL Query(LL x,LL y){
	LL ret(0);
	LL fx(top[x]),fy(top[y]);
	while(fx!=fy){
		if(dep[fx]>=dep[fy]){
			ret+=Bt.Query(id[fx],id[x]); x=fa[fx];
		}else{
			ret+=Bt.Query(id[fy],id[y]); y=fa[fy];
		}
		fx=top[x]; fy=top[y];
	}
	if(dep[x]<=dep[y])
		ret+=Bt.Query(id[x],id[y])-val[x];
	else
		ret+=Bt.Query(id[y],id[x])-val[y];
	return ret;
}
int main(){
	n=Read(); m=Read();
	for(LL i=1;i<=n;++i){
		LL u(Read()),v(Read()),w(Read());
		Add(u,v,w); Add(v,u,w);
		e[i]=(E){u,v,w};
	}
	Dfs1(1,0); Dfs2(1,1);
	for(LL i=1;i<=n;++i)
	    Bt.Add(id[i],val[i]);
	while(m--){
		LL op(Read()),x(Read()),y(Read());
		if(op==1){
			if(x==n_tree){
				n_d=y;
				continue;
			}
			LL v(bel[x]);
			Bt.Add(id[v],-val[v]);
			Bt.Add(id[v],val[v]=y);
		}else{
			printf("%d
",std::min(Query(x,y),std::min(Query(x,n_u)+Query(y,n_v)+n_d,Query(x,n_v)+Query(y,n_u)+n_d)));
		}
	}
	return 0;
}