P4114 Qtree1

Posted 2022-12-22 qyj060604

P4114 Qtree1

直接树剖

然后SB地dfs1打挂

代码：

#include<bits/stdc++.h>
using namespace std;
const int N=100005;
typedef long long ll;
struct line
    int from,to;
    ll val;
    int conec;
s[N];
int n;
int hed[N],tal[N<<1],nxt[N<<1],cnt=0;
ll val[N<<1];
int fa[N];
int dep[N];
int size[N]=0;
int son[N]=0;
int dfn[N];
int rk[N];
int indexy=0;
int top[N];
ll v[N];
ll llmax(ll x,ll y)return x>y?x:y;
struct Sugment_Tree
    ll t[N<<2];
    #define mid (l+r)/2
    void push_up(int num)
        t[num]=llmax(t[num<<1],t[num<<1|1]);
    
    void build(int l,int r,int num)
        if(l==r)
            t[num]=v[l];
            return;
        
        build(l,mid,num<<1),build(mid+1,r,num<<1|1);
        push_up(num);
    
    void upd(int l,int r,int num,int pos,ll SUM)
        if(l>pos||r<pos) return;
        if(l==r&&r==pos)
            t[num]=SUM;
            return;
        
        upd(l,mid,num<<1,pos,SUM);
        upd(mid+1,r,num<<1|1,pos,SUM);
        push_up(num);
     
    ll ask(int l,int r,int num,int L,int R)
        if(l>R||r<L) return 0;
        if(l>=L&&r<=R) return t[num];
        return llmax(ask(l,mid,num<<1,L,R),ask(mid+1,r,num<<1|1,L,R));
    
T;
void addege(int x,int y,ll z)
    cnt++;
    tal[cnt]=y;
    val[cnt]=z;
    nxt[cnt]=hed[x];
    hed[x]=cnt;

void dfs1(int u,int pa)
    fa[u]=pa;
    size[u]=1;
    for(int i=hed[u];i;i=nxt[i])
        int v=tal[i];
        if(v==fa[u]) continue;
        dep[v]=dep[u]+1;
        dfs1(v,u);
        size[u]+=size[v];
        if(size[v]>size[son[u]]) son[u]=v;
    

void dfs2(int u,int tp)
    indexy++;
    dfn[u]=indexy;
    rk[dfn[u]]=u;
    top[u]=tp;
    if(!son[u]) return;
    dfs2(son[u],tp);
    for(int i=hed[u];i;i=nxt[i])
        int v=tal[i];
        if(v==fa[u]||v==son[u]) continue;
        dfs2(v,v);
    


ll cgn(int x,int y)
    ll ans=0;
    //LCA不能算进来！！！！！！ 
    while(top[x]!=top[y])
        if(dep[top[x]]<dep[top[y]]) swap(x,y);
        ans=llmax(ans,T.ask(1,n,1,dfn[top[x]],dfn[x]));
        x=fa[top[x]];
    
    if(dep[x]<dep[y]) swap(x,y);
    ans=llmax(ans,T.ask(1,n,1,dfn[y]+1,dfn[x]));
    return ans;

int main()
    scanf("%d",&n);
    for(int i=1;i<n;i++)
        scanf("%d%d%lld",&s[i].from,&s[i].to,&s[i].val);    
        addege(s[i].from,s[i].to,s[i].val);
        addege(s[i].to,s[i].from,s[i].val);
    
    dep[1]=1;
    dfs1(1,1);
    dfs2(1,1);
    for(int i=1;i<n;i++)
        if(fa[s[i].from]==s[i].to) v[dfn[s[i].from]]=s[i].val,s[i].conec=dfn[s[i].from];
        else v[dfn[s[i].to]]=s[i].val,s[i].conec=dfn[s[i].to];
     
    /*
    for(int i=1;i<=n;i++)
        cout<<v[i]<<" ";
    cout<<endl;
    */
    T.build(1,n,1);
    char c[10];
    while(1)
        scanf("%s",c);
        if(c[0]==‘D‘) break;
        else if(c[0]==‘Q‘)
            int x,y;
            scanf("%d%d",&x,&y);
            if(x==y)
                printf("0\n");
                continue;
            
            printf("%lld\n",cgn(x,y));
        
        else
            int pos;
            ll va;
            scanf("%d%lld",&pos,&va);
            T.upd(1,n,1,s[pos].conec,va);
        
    
    return 0;