BZOJ 4326 树链剖分+二分+差分+记忆化

去年NOIP的时候我还不会树链剖分！

还是被UOJ 的数据卡了一组。

差分的思想还是很神啊！

 #include <iostream>
 #include <cstring>
 #include <cstdio>
 #include <algorithm>
 #include <ctime>
 #include <cstdlib>
 using namespace std;
 const int Maxn=;
 const int Inf=0x3f3f3f3f;
 int n,m,u,v,w,cnt,tot,MaxLen,MinLen,Minw,Maxw,Ans;
 int head[Maxn],dep[Maxn],siz[Maxn],father[Maxn],W[Maxn],p[Maxn],q[Maxn],dis[Maxn],Len[Maxn],c[Maxn],top[Maxn],Memory[Maxn],Root;
 struct Edge{int to,next,w;}edge[Maxn<<];
 inline void Get_Int(int &x)
 {
     x=;  char ch=getchar(); int f=;
     while (ch<'' || ch>'') {if (ch=='-') f=-; ch=getchar();}
     while (ch>='' && ch<='') {x=x*+ch-''; ch=getchar();} x*=f;
 }
 inline void Put_Int(int x)
 {
     char ch[];  int top=;
     if (x==) ch[++top]='';
     while (x) ch[++top]=x%+'',x/=;
     while (top) putchar(ch[top--]); putchar('\n');
 }
 inline int Max(int x,int y) {return x>y?x:y;}
 inline int Min(int x,int y) {return x>y?y:x;}
 inline void Add(int u,int v,int w)
 {edge[cnt].to=v;edge[cnt].next=head[u];edge[cnt].w=w;head[u]=cnt++;}
 //==============================================
 void Dfs1(int u,int fa)
 {
     siz[u]=;
     for (int i=head[u];i!=-;i=edge[i].next)
         if (edge[i].to!=fa)
         {
             dep[edge[i].to]=dep[u]+;
             father[edge[i].to]=u;
             dis[edge[i].to]=dis[u]+edge[i].w;
             W[edge[i].to]=edge[i].w;
             Dfs1(edge[i].to,u);
             siz[u]+=siz[edge[i].to];
         }
 }
 void Dfs2(int u,int chain,int fa)
 {
     top[u]=chain;  int k=;
     for (int i=head[u];i!=-;i=edge[i].next)
         if (edge[i].to!=fa && (siz[edge[i].to]>siz[k] || k==)) k=edge[i].to;
     if (k==) return;
     Dfs2(k,chain,u);
     for (int i=head[u];i!=-;i=edge[i].next)
         if (edge[i].to!=fa && k!=edge[i].to) Dfs2(edge[i].to,edge[i].to,u);
 }
 inline int Lca(int u,int v)
 {
     while (true)
     {
         if (top[u]==top[v]) return dep[u]>dep[v]?v:u;
         if (dep[top[u]]>dep[top[v]]) u=father[top[u]]; else v=father[top[v]];
     }
 }
 int Get(int u,int f)
 {
     for (int i=head[u];i!=-;i=edge[i].next)
         if (f!=edge[i].to)
             c[u]+=Get(edge[i].to,u);
     if (c[u]==tot) MinLen=Max(MinLen,W[u]);
     return c[u];
 }
 inline bool Check(int t)
 {
     MaxLen=MinLen=tot=;
     memset(c,,sizeof(c));
     for (int i=;i<=m;i++)
         if (Len[i]>t)
         {
             c[p[i]]++,c[q[i]]++;
             c[Lca(p[i],q[i])]-=;
             MaxLen=Max(MaxLen,Len[i]);
             tot++;
         }
     if (Memory[tot])
     {
         if (Memory[tot]<=t) return true;
         return false;
     }
     Get(Root,Root);
     Memory[tot]=(MaxLen-MinLen);
     if (Memory[tot]<=t) return true;
     return false;
 }
 int main()
 {
     srand(time());
     Get_Int(n),Get_Int(m);
     memset(head,-,sizeof(head)); Minw=Inf;
     for (int i=;i<n;i++)
     {
         Get_Int(u),Get_Int(v),Get_Int(w);
         Add(u,v,w),Add(v,u,w);
         Minw=Min(Minw,w);
     }
     for (int i=;i<=m;i++) Get_Int(p[i]),Get_Int(q[i]);
     Root=rand()%n+;
     father[Root]=Root; dep[Root]=; dis[Root]=;
     Dfs1(Root,Root);
     Dfs2(Root,Root,Root);
     memset(Memory,,sizeof(Memory));
     for (int i=;i<=m;i++) Len[i]=dis[p[i]]+dis[q[i]]-*dis[Lca(p[i],q[i])],Maxw=Max(Maxw,Len[i]);
     int l=Minw,r=Maxw;
     while (l<=r)
     {
         int mid=(l+r)>>;
         if (Check(mid)) Ans=mid,r=mid-; else l=mid+;

     }
     Put_Int(Ans);
     return ;
 }

C++