P4114 Qtree1

思路

树剖一发，注意对LCA的处理

代码

#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
const int MAXN = 100100;
int dfs_clock,dep[MAXN*2],heason[MAXN*2],id[MAXN*2],sz[MAXN*2],top[MAXN*2],fa[MAXN*2],w_p[MAXN*2],v[MAXN*2],fir[MAXN*2],nxt[MAXN*2],w[MAXN*2],val[MAXN*2],maxx[MAXN*5],cnt;
struct Edge{
    int u,v,w;
}E[MAXN*2];

void addedge(int ui,int vi,int wi){
    ++cnt;
    v[cnt]=vi;
    w[cnt]=wi;
    nxt[cnt]=fir[ui];
    fir[ui]=cnt;
}
void dfs1(int u,int f,int wx){
    fa[u]=f;
    sz[u]=1;
    w_p[u]=wx;
    for(int i=fir[u];i;i=nxt[i]){
        if(v[i]==f)
            continue;
        dep[v[i]]=dep[u]+1;
        dfs1(v[i],u,w[i]);
        sz[u]+=sz[v[i]];
        if(heason[u]==0||sz[v[i]]>sz[heason[u]])
            heason[u]=v[i];
    }
}
void dfs2(int u,int f,int topf){
    id[u]=++dfs_clock;
    val[id[u]]=w_p[u];
    top[u]=topf;
    if(!heason[u])
        return;
    dfs2(heason[u],u,topf);
    for(int i=fir[u];i;i=nxt[i]){
        if(v[i]==f||v[i]==heason[u])
            continue;
        dfs2(v[i],u,v[i]);
    }
}
void pushup(int o){
    maxx[o]=max(maxx[o<<1],maxx[o<<1|1]);
}
void build(int l,int r,int o){
    if(l==r){
        maxx[o]=val[l];
        return;
    }
    int mid=(l+r)>>1;
    build(l,mid,o<<1);
    build(mid+1,r,o<<1|1);
    pushup(o);
}
void update(int l,int r,int pos,int o,int c){
    if(l==r){
        maxx[o]=c;
        return;
    }
    int mid=(l+r)>>1;
    if(pos<=mid)
        update(l,mid,pos,o<<1,c);
    else
        update(mid+1,r,pos,o<<1|1,c);
    pushup(o);
}
void update(int o,int c){
    update(1,dfs_clock,id[o],1,c);
}
int query(int L,int R,int l,int r,int o){
    if(L<=l&&r<=R)
        return maxx[o];
    int mid=(l+r)>>1,ans=0;
    if(L<=mid)
        ans=max(ans,query(L,R,l,mid,o<<1));
    if(R>mid)
        ans=max(ans,query(L,R,mid+1,r,o<<1|1));
    return ans;
}
int query(int x,int y){
    int ans=0;
    while(top[x]!=top[y]){
        if(dep[top[x]]<dep[top[y]])
            swap(x,y);
        ans=max(ans,query(id[top[x]],id[x],1,dfs_clock,1));
        x=fa[top[x]];
    }
    if(dep[x]>dep[y])
        swap(x,y);
    ans=max(ans,query(id[x],id[y],1,dfs_clock,1));
    return ans;
}
int lca(int x,int y){
    while(top[x]!=top[y]){
        if(dep[top[x]]<dep[top[y]])
            swap(x,y);
        x=fa[top[x]];
    }
    return (dep[x]<dep[y])?x:y;
}
int n;
int main(){
    scanf("%d",&n);
    for(int i=1;i<n;i++){
        scanf("%d %d %d",&E[i].u,&E[i].v,&E[i].w);
        addedge(E[i].u,E[i].v,E[i].w);
        addedge(E[i].v,E[i].u,E[i].w);
    }
    dfs1(1,0,0);
    dfs2(1,0,1);
    build(1,dfs_clock,1);
    char opt[10];
    while(1){
        scanf("%s",&opt);
        if(opt[0]=='D')
            break;
        if(opt[0]=='Q'){
            int a,b;
            scanf("%d %d",&a,&b);
            int LCA=lca(a,b);
            // printf("lca=%d\n",LCA);
            int t=w_p[LCA];
            update(LCA,0);
            int ans=query(a,b);
            update(LCA,t);
            printf("%d\n",ans);
        }
        else{
            int a,b;
            scanf("%d %d",&a,&b);
            int t=(dep[E[a].u]>dep[E[a].v])?E[a].u:E[a].v;
            w_p[t]=b;
            update(t,b);
        }
    }
    return 0;
}