bzoj4390[Usaco2015 dec]Max Flow*

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #define inc(i,j,k) for(int i=j;i<=k;i++)
 5 #define maxn 50010
 6 using namespace std;
 7 
 8 inline int read(){
 9     char ch=getchar(); int f=1,x=0;
10     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1; ch=getchar();}
11     while(ch>=‘0‘&&ch<=‘9‘)x=x*10+ch-‘0‘,ch=getchar();
12     return f*x;
13 }
14 int sm[maxn],sz[maxn],dep[maxn],fa[maxn],top[maxn],pos[maxn],n,q,ans,tot;
15 struct e{int t,n;}es[maxn*2]; int g[maxn],ess;
16 void pe(int f,int t){es[++ess]=(e){t,g[f]}; g[f]=ess; es[++ess]=(e){f,g[t]}; g[t]=ess;}
17 void dfs1(int x,int f){
18     sz[x]=1;
19     for(int i=g[x];i;i=es[i].n)if(es[i].t!=f){
20         fa[es[i].t]=x; dep[es[i].t]=dep[x]+1; dfs1(es[i].t,x); sz[x]+=sz[es[i].t];
21     }
22 }
23 void dfs2(int x,int f,int tp){
24     pos[x]=++tot; top[x]=tp; int mx1=0,mx2=0;
25     for(int i=g[x];i;i=es[i].n)if(es[i].t!=f&&sz[es[i].t]>mx1)mx1=sz[es[i].t],mx2=es[i].t;
26     if(!mx2)return; dfs2(mx2,x,tp);
27     for(int i=g[x];i;i=es[i].n)if(es[i].t!=f&&es[i].t!=mx2)dfs2(es[i].t,x,es[i].t);
28 }
29 void solve(int x,int y){
30     for(;top[x]!=top[y];sm[pos[top[x]]]++,sm[pos[x]+1]--,x=fa[top[x]])if(dep[top[x]]<dep[top[y]])swap(x,y);
31     if(dep[x]>dep[y])swap(x,y); sm[pos[x]]++; sm[pos[y]+1]--;
32 }
33 int main(){
34     n=read(); q=read(); inc(i,1,n-1){int x=read(),y=read(); pe(x,y);} dfs1(1,0); dfs2(1,0,1);
35     inc(i,1,q){int x=read(),y=read(); solve(x,y);}
36     inc(i,1,n)sm[i]+=sm[i-1],ans=max(ans,sm[i]); printf("%d",ans); return 0;
37 }