bzoj1036

Posted 2020-10-16 宣毅鸣

题解：

树链剖分的模板题

具体代码详见网上的其他代码

代码：

#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=400005;
char s[100];
int data[N],p[N],n,pos,fp[N],num[N];
int x,y,z,tot,top[N],T,e[N][3],val[N],deep[N],son[N],fa[N],ne[N],fi[N],zz[N];
void jb(int x,int y)
{
    ne[++tot]=fi[x];
    fi[x]=tot;
    zz[tot]=y;
}
void dfs1(int x,int y,int z)
{
    deep[x]=z;
    fa[x]=y;
    for (int i=fi[x];i;i=ne[i])
     {
         int k=zz[i];
         if (k!=y)
          {
              dfs1(k,x,z+1);
              num[x]+=num[k];
              if (son[x]==-1||(num[son[x]]<num[k]))son[x]=k;
          }
     }
}
void dfs2(int x,int y)
{
    top[x]=y;
    if (son[x]!=-1)
     {
         p[x]=pos++;
         fp[p[x]]=x;
         dfs2(son[x],y);
     }
    else
     {
         p[x]=pos++;
         fp[p[x]]=x;
         return;
     } 
    for (int i=fi[x];i;i=ne[i])
     if (zz[i]!=son[x]&&zz[i]!=fa[x])
      dfs2(zz[i],zz[i]); 
}
void pushup(int x)
{
    data[x]=max(data[x*2],data[x*2+1]);
}
void build(int l,int r,int x)
{
    if (l==r)
     {
         data[x]=val[l];
         return;
     }
    int mid=(l+r)/2; 
    build(l,mid,x*2); 
    build(mid+1,r,x*2+1);
    pushup(x);
}
void updata(int p,int q,int l,int r,int x)
{
    if (l==r)
     {
         data[x]=q;
         return;
     }
    int mid=(l+r)/2;
    if (p<=mid)updata(p,q,l,mid,x*2);
    else updata(p,q,mid+1,r,x*2+1);
    pushup(x); 
}
int query(int x,int y,int l,int r,int s)
{
    if (x>r||y<l)return 0;
    if (x<=l&&y>=r)return data[s];
    int mid=(l+r)/2;
    return max(query(x,y,l,mid,s*2),query(x,y,mid+1,r,s*2+1));
}
int find(int x,int y)
{
    int f1=top[x],f2=top[y],temp=0;
    while (f1!=f2)
     {
         if (deep[f1]<deep[f2])
          {
              swap(x,y);
              swap(f1,f2);
          }
         temp=max(temp,query(p[f1],p[x],1,n,1)); 
         x=fa[f1],f1=top[x]; 
     }
    if (x==y)return temp;
    if (deep[x]>deep[y])swap(x,y);
    return max(temp,query(p[son[x]],p[y],1,n,1)); 
}
int read()
{
    int x=0;char c;
    for (;c<‘0‘||c>‘9‘;c=getchar());
    for (;c>=‘0‘&&c<=‘9‘;c=getchar())x=x*10+c-48;
    return x;
}
int main()
{
    scanf("%d",&T);
    while (T--)
     {
         pos=1;tot=0;
         memset(fi,0,sizeof fi);
         memset(son,-1,sizeof son);
         memset(data,0,sizeof data);
         scanf("%d",&n);
         for (int i=0;i<n-1;i++)
          {
              scanf("%d%d%d",&e[i][0],&e[i][1],&e[i][2]);
              jb(e[i][0],e[i][1]);jb(e[i][1],e[i][0]);
          }
         dfs1(1,0,0);
        dfs2(1,1);
        for (int i=0;i<n-1;i++)
         {
             if (deep[e[i][0]]<deep[e[i][1]])swap(e[i][0],e[i][1]);
             val[p[e[i][0]]]=e[i][2];
         } 
        build(1,n,1); 
         while (scanf("%s",&s))
          {
              if (s[0]==‘D‘)break;
              x=read();y=read();
              if (s[0]==‘Q‘)printf("%d\n",find(x,y));
              else updata(p[e[x-1][0]],y,1,n,1);
          }
     }
    return 0; 
}