深搜，windows下会死。,Linux下就过了对不对？
#include<bits/stdc++.h>
const long long maxn=4e6+1;
inline const void read(long long &a)
{
char c=getchar();a=0;
while(c<'0'||c>'9')c=getchar();
while(c>='0'&&c<='9')
{
a=(a<<1)+(a<<3)+c-'0';
c=getchar();
}
}
long long n,d=0,kk=1;
long long point[maxn],next[maxn],father[maxn],to[maxn],ans[maxn],num[maxn],sum[maxn],deep[maxn];
bool vis[maxn];
inline const void add(long long a,long long b)
{
next[++d]=point[a];
point[a]=d;
to[d]=b;
}
inline const void dfs1(long long p)
{
vis[p]=true;
long long side=point[p];
num[p]=1;sum[p]+=deep[p];
while(side)
{
if(!vis[to[side]])
{
father[to[side]]=p;
deep[to[side]]=deep[p]+1;
dfs1(to[side]);
num[p]+=num[to[side]];sum[p]+=sum[to[side]];
}
side=next[side];
}
}
inline const void dfs2(long long p)
{

if(p!=1)ans[p]=ans[father[p]]-2*num[p]+num[1];
if(ans[p]>ans[kk])kk=p;
if(ans[p]==ans[kk]&&p<kk)kk=p;
vis[p]=true;
long long side=point[p];
while(side)
{
if(!vis[to[side]])dfs2(to[side]);
side=next[side];
}
}
int main()
{
memset(father,0,sizeof(father));
memset(sum,0,sizeof(sum));
memset(point,0,sizeof(point));
memset(ans,0,sizeof(ans));
read(n);
long long u,v;
for(long long i=1;i<=n-1;i++){read(u);read(v);add(u,v);add(v,u);}
deep[1]=0;
memset(vis,false,sizeof(vis));
dfs1(1);
memset(vis,false,sizeof(vis));ans[1]=sum[1];
dfs2(1);
std::cout<<kk;
return 0;
}
这样就可以过windows了
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
#define rep(i,l,r) for (int i=l; i<=r; i++)
#define drep(i,r,l) for (int i=r; i>=l; i--)
#define ll long long
#define pb push_bake
const int N = 1000008;
int n, tot, head[N], h[N], fa[N], sum[N];
bool vis[N];
ll Down[N], Up[N];
int read()
{
char c; int w = 1, num = 0;
for (c = getchar(); !isdigit(c) && c != '+' && c != '-'; c = getchar());
if (c == '-') c = getchar(), w = -1;
if (c == '+') c = getchar();
for (; isdigit(c); c = getchar()) num = num * 10 + c - '0';
return num * w;
}
struct Node
{
int next, node;
}e[2 * N];
inline void add(int x, int y)
{
e[++tot].next = head[x], head[x] = tot, e[tot].node = y;
e[++tot].next = head[y], head[y] = tot, e[tot].node = x;
}
void topsort()
{
int l = 1, r = 1;
h[1] = 1; vis[1] = 1;
while (l <= r)
{
int u = h[l++];
for (int i = head[u], v; v = e[i].node, i; i = e[i].next)
if (!vis[v])
{
vis[v] = 1;
fa[v] = u;
h[++r] = v;
}
}
}
int main()
{
n = read();
rep(i, 1, n - 1)
{
int u, v;
u = read(); v = read();
add(u, v);
}

topsort();
drep(k, n, 1)
{
int u = h[k];
sum[u] = 1;
for (int i = head[u], v; v = e[i].node, i; i = e[i].next)
if (v != fa[u])
{
sum[u] += sum[v];
Down[u] += Down[v] + sum[v];
}
}
rep(k, 2, n)
{
int u = h[k];
Up[u] += Up[fa[u]] + sum[1] - sum[fa[u]] + 1;
Up[u] += Down[fa[u]] - Down[u] - sum[u] + sum[fa[u]] - sum[u] - 1;
}
ll Max = 0; int ans;
rep(i, 1, n) if (Up[i] + Down[i] > Max) Max = Up[i] + Down[i], ans = i;
printf("%d\n", ans);
return 0;
}