[BZOJ3083]遥远的国度（链剖+dfs序）

题目描述

题解

代码

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;

const int max_n=200100;
const int max_sum=max_n*5;
const int max_e=max_n*2;
const int INF=2147483647;

int n,m,x,y,opt,id,p1,p2,val;
int w[max_n];
int N,root,ans;
int tot,point[max_n],next[max_e],v[max_e];
int sum[max_sum],delta[max_sum];
int father[max_n],son[max_n],h[max_n],size[max_n];
int top[max_n],in[max_n],out[max_n],num[max_n];

inline void addedge(int x,int y){
++tot; next[tot]=point[x]; point[x]=tot; v[tot]=y;
++tot; next[tot]=point[y]; point[y]=tot; v[tot]=x;
}

inline void dfs_1(int x,int fa,int dep){
size[x]=1; h[x]=dep; father[x]=fa;
int maxson=0;

for (int i=point[x];i;i=next[i])
if (v[i]!=fa){
dfs_1(v[i],x,dep+1);

size[x]+=size[v[i]];
if (size[v[i]]>maxson){
maxson=size[v[i]];
son[x]=v[i];
}
}
}

inline void dfs_2(int x,int fa){
if (son[fa]!=x) top[x]=x;
else top[x]=top[fa];

in[x]=++N;

if (son[x]) dfs_2(son[x],x);

for (int i=point[x];i;i=next[i])
if (v[i]!=fa&&v[i]!=son[x])
dfs_2(v[i],x);

out[x]=N;
}

inline void update(int now){
sum[now]=min(sum[now<<1],sum[now<<1|1]);
}

inline void pushdown(int now,int l,int r,int mid){
if (delta[now]){

sum[now<<1]=delta[now];
delta[now<<1]=delta[now];

sum[now<<1|1]=delta[now];
delta[now<<1|1]=delta[now];

delta[now]=0;
}
}

inline void build(int now,int l,int r){
int mid=(l+r)>>1;

if (l==r){
sum[now]=w[num[l]];
return;
}

build(now<<1,l,mid);
build(now<<1|1,mid+1,r);

update(now);
}

inline void interval_change(int now,int l,int r,int lrange,int rrange,int v){
int mid=(l+r)>>1;

if (lrange<=l&&r<=rrange){
sum[now]=v;
delta[now]=v;
return;
}

pushdown(now,l,r,mid);

if (lrange<=mid)
interval_change(now<<1,l,mid,lrange,rrange,v);
if (mid+1<=rrange)
interval_change(now<<1|1,mid+1,r,lrange,rrange,v);

update(now);
}

inline int query(int now,int l,int r,int lrange,int rrange){
int mid=(l+r)>>1,ans=INF;

if (lrange<=l&&r<=rrange) return sum[now];

pushdown(now,l,r,mid);

if (lrange<=mid)
ans=min(ans,query(now<<1,l,mid,lrange,rrange));
if (mid+1<=rrange)
ans=min(ans,query(now<<1|1,mid+1,r,lrange,rrange));

return ans;
}

inline void CHANGE(){
int f1=top[p1],f2=top[p2];

while (f1!=f2){

if (h[f1]<h[f2]){
swap(f1,f2);
swap(p1,p2);
}

interval_change(1,1,N,in[f1],in[p1],val);
p1=father[f1];
f1=top[p1];
}

if (in[p1]>in[p2]) swap(p1,p2);
interval_change(1,1,N,in[p1],in[p2],val);
}

inline void QUERY(){

if (id==root){
ans=query(1,1,N,1,N);
printf("%d\n",ans);
return;
}

if (in[root]<in[id]||in[root]>out[id]){
ans=query(1,1,N,in[id],out[id]);
printf("%d\n",ans);
return;
}

for (int i=point[id];i;i=next[i])
if (v[i]!=father[id]&&in[root]>=in[v[i]]&&in[root]<=out[v[i]]){
ans=query(1,1,N,1,in[v[i]]-1);
if (out[v[i]]!=N) ans=min(ans,query(1,1,N,out[v[i]]+1,N));
printf("%d\n",ans);
return;
}
}

int main(){
scanf("%d%d",&n,&m);
for (int i=1;i<n;++i){
scanf("%d%d",&x,&y);
addedge(x,y);
}
for (int i=1;i<=n;++i)
scanf("%d",&w[i]);

scanf("%d",&id);
root=id;
dfs_1(id,0,1);
dfs_2(id,0);

for (int i=1;i<=n;++i)
num[in[i]]=i;

build(1,1,N);

for (int i=1;i<=m;++i){
scanf("%d",&opt);
switch(opt){

case 1:{
scanf("%d",&id);
root=id;
break;
}

case 2:{
scanf("%d%d%d",&p1,&p2,&val);
CHANGE();
break;
}

case 3:{
scanf("%d",&id);
QUERY();
break;
}
}
}
return 0;
}

总结