【块状树】【LCA】bzoj1787 [Ahoi2008]Meet 紧急集合

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cmath>
 4 using namespace std;
 5 #define maxn 500001
 6 struct Graph
 7 {int v[maxn<<1],first[maxn<<1],next[maxn<<1],w[maxn<<1],en;
 8 void AddEdge(const int &a,const int &b)
 9 {v[++en]=b;next[en]=first[a];first[a]=en;}}G;
10 int dep[maxn],fa[maxn],top[maxn],siz[maxn],x,y,z,sz,n,m;
11 int Abs(const int &x){return x<0 ? (-x) : x;}
12 int Res,Num;char C,CH[12];
13 inline int R()
14 {
15     Res=0;C=‘*‘;
16     while(C<‘0‘||C>‘9‘)C=getchar();
17     while(C>=‘0‘&&C<=‘9‘){Res=Res*10+(C-‘0‘);C=getchar();}
18     return Res;
19 }
20 inline void P(long long x)
21 {
22     Num=0;if(!x){putchar(‘0‘);return;}
23     while(x>0)CH[++Num]=x%10,x/=10;
24     while(Num)putchar(CH[Num--]+48);
25 }
26 void makeblock(int cur)
27 {
28     for(int i=G.first[cur];i;i=G.next[i])
29       if(G.v[i]!=fa[cur])
30         {
31           dep[G.v[i]]=dep[cur]+1;
32           fa[G.v[i]]=cur;
33           if(siz[top[cur]]<sz)
34             {
35               siz[top[cur]]++;
36               top[G.v[i]]=top[cur];
37             }
38           makeblock(G.v[i]);
39         }
40 }
41 inline int QLCA(int u,int v)
42 {
43     while(u!=v)
44       {
45         if(top[u]==top[v])
46           {
47             if(dep[u]<dep[v]) swap(u,v);
48             u=fa[u];
49           }
50         else
51           {
52             if(dep[top[u]]<dep[top[v]]) swap(u,v);
53             u=fa[top[u]];
54           }
55       }
56     return u;
57 }
58 int main()
59 {
60     n=R();m=R();
61     for(int i=1;i<n;i++)
62       {
63         x=R();y=R();
64         G.AddEdge(x,y);
65         G.AddEdge(y,x);
66       }
67     for(int i=1;i<=n;i++) {top[i]=i; siz[i]=1;}
68     sz=sqrt((double)n*5.0); makeblock(1);
69     for(;m>0;m--)
70       {
71         x=R();y=R();z=R();
72         int f1=QLCA(x,y),f2=QLCA(x,z),f3=QLCA(y,z);
73         if(f1==f2)
74           {
75             int f4=QLCA(x,f3); P(f3); putchar(‘ ‘);
76             P(Abs(dep[f3]-dep[y])+Abs(dep[f3]-dep[z])
77             +Abs(dep[f4]-dep[x])+Abs(dep[f4]-dep[f3])); puts("");
78           }
79         else if(f1==f3)
80           {
81             int f4=QLCA(y,f2); P(f2); putchar(‘ ‘);
82             P(Abs(dep[f2]-dep[x])+Abs(dep[f2]-dep[z])
83             +Abs(dep[f4]-dep[y])+Abs(dep[f4]-dep[f2])); puts("");
84           }
85         else
86           {
87             int f4=QLCA(z,f1); P(f1); putchar(‘ ‘);
88             P(Abs(dep[f1]-dep[x])+Abs(dep[f1]-dep[y])
89             +Abs(dep[f4]-dep[z])+Abs(dep[f4]-dep[f1])); puts("");
90           }
91       }
92     return 0;
93 }