This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 17;
int n, sz[N], ans, ti;
vector <int> adj[N];
multiset <int> in, out;
void dfs (int u, int pr)
{
++sz[u];
for (int v: adj[u])
{
if (v == pr)
{
continue;
}
dfs (v, u);
sz[u] += sz[v];
}
}
void calc (int u, int pr)
{
if (u > 1)
{
int a, b, c;
auto x = out.lower_bound (sz[u]);
out.erase (x);
x = in.upper_bound ((n - sz[u]) / 2 + sz[u]);
if (x != in.begin())
{
--x;
a = n - *x, b = *x - sz[u], c = sz[u];
ans = min (ans, max ({abs (a - b), abs (b - c), abs (c - a)}));
++x;
}
if (x != in.end())
{
++x;
if (x != in.end())
{
a = n - *x, b = *x - sz[u], c = sz[u];
ans = min (ans, max ({abs (a - b), abs (b - c), abs (c - a)}));
}
--x;
}
if (x != in.end())
{
a = n - *x, b = *x - sz[u], c = sz[u];
ans = min (ans, max ({abs (a - b), abs (b - c), abs (c - a)}));
}
x = out.upper_bound ((n - sz[u]) / 2);
if (x != out.begin())
{
--x;
a = n - *x - sz[u], b = *x, c = sz[u];
ans = min (ans, max ({abs (a - b), abs (b - c), abs (c - a)}));
++x;
}
if (x != out.end())
{
++x;
if (x != out.end())
{
a = n - *x - sz[u], b = *x, c = sz[u];
ans = min (ans, max ({abs (a - b), abs (b - c), abs (c - a)}));
}
--x;
}
if (x != out.end())
{
a = n - *x - sz[u], b = *x, c = sz[u];
ans = min (ans, max ({abs (a - b), abs (b - c), abs (c - a)}));
}
in.insert (sz[u]);
}
for (int v: adj[u])
{
if (v == pr)
{
continue;
}
calc (v, u);
}
if (u > 1)
{
auto x = in.lower_bound (sz[u]);
in.erase (x);
out.insert (sz[u]);
}
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n;
for (int i = 1, u, v; i < n; ++i)
{
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
dfs (1, 0);
for (int i = 2; i <= n; ++i)
{
out.insert (sz[i]);
}
ans = 1e9;
calc (1, 0);
cout << ans;
}
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