Submission #94107

#	Time	Username	Problem	Language	Result	Execution time	Memory
94107		qkxwsm	Shymbulak (IZhO14_shymbulak)	C++14	0 / 100	146 ms	18928 KiB

shymbulak

#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/rope>

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

random_device(rd);
mt19937 rng(rd());
const long long FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();

struct custom_hash
{
	template<class T>
	unsigned long long operator()(T v) const
	{
		unsigned long long x = v;
		x += FIXED_RANDOM;
		// x += 11400714819323198485ull;
		// x = (x ^ (x >> 30)) * 13787848793156543929ull;
		x = (x ^ (x >> 27)) * 10723151780598845931ull;
		return x ^ (x >> 31);
	}
};

template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<class T, class U> using hash_table = gp_hash_table<T, U, custom_hash>;

template<class T>
T randomize(T mod)
{
	return (uniform_int_distribution<T>(0, mod - 1))(rng);
}
template<class T>
void readi(T &x)
{
	x = 0;
	bool negative = false;
	char c = ' ';
	while (c < '-')
	{
		c = getchar();
	}
	if (c == '-')
	{
		negative = true;
		c = getchar();
	}
	while (c >= '0')
	{
		x = x * 10 + (c - '0');
		c = getchar();
	}
	if (negative)
	{
		x = -x;
	}
}
template<class T>
void printi(T output)
{
	if (output == 0)
	{
		putchar('0');
		return;
	}
	if (output < 0)
	{
		putchar('-');
		output = -output;
	}
	int buf[20], n = 0;
	while(output)
	{
		buf[n] = ((output % 10));
		output /= 10;
		n++;
	}
	for (n--; n >= 0; n--)
	{
		putchar(buf[n] + '0');
	}
	return;
}
template<class T>
void ckmin(T &a, T b)
{
	a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
	a = max(a, b);
}
long long expo(long long a, long long e, long long mod)
{
	return ((e == 0) ? 1 : ((expo(a * a % mod, e >> 1, mod)) * ((e & 1) ? a : 1) % mod));
}
template<class T, class U>
void nmod(T &x, U mod)
{
	if (x >= mod) x -= mod;
}
template<class T>
T gcd(T a, T b)
{
	return (b ? gcd(b, a % b) : a);
}

#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define PB push_back
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define DBG(x) cerr << #x << " = " << (x) << endl
#define SZ(x) ((int) ((x).size()))
#define FOR(i, a, b) for (auto i = (a); i < (b); i++)
#define FORD(i, a, b) for (auto i = (a) - 1; i >= (b); i--)
#define ALL(x) (x).begin(), (x).end()

const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-9;

#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 200013

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<ld> vd;
typedef vector<pii> vpi;
typedef vector<pll> vpl;
typedef vector<pdd> vpd;

int U, V, N, M;
int dsu[MAXN];
int parent[MAXN], depth[MAXN];
vi edge[MAXN], edge1[MAXN];
vi cyc;
bitset<MAXN> inside;
pii dp[MAXN], dp1[MAXN];
int diam = 0;
ll ans;
vi nodes;
vector<pair<int, ll> > res;

int get(int u)
{
	return (u == dsu[u] ? u : dsu[u] = get(dsu[u]));
}
void DFS(int u)
{
	for (int v : edge[u])
	{
		if (v == parent[u]) continue;
		if (u == U && v == V) continue;
		if (u == V && v == U) continue;
		parent[v] = u;
		// cerr << u << " -> " << v << endl;
		DFS(v);
	}
}
bool merge(int u, int v)
{
	u = get(u);
	v = get(v);
	if (u == v) return false;
	dsu[u] = v;
	return true;
}
void solve(int u, int w)
{
	nodes.PB(u);
	dp[u] = {0, 1};
	for (int v : edge[u])
	{
		if (v == w || inside[v]) continue;
		edge1[v].PB(u);
		edge1[u].PB(v);
		solve(v, u);
		if (dp[v].fi + 1 > dp[u].fi)
		{
			dp[u].fi = dp[v].fi + 1;
			dp[u].se = dp[v].se;
		}
		else if (dp[v].fi + 1 == dp[u].fi)
		{
			dp[u].se += dp[v].se;
		}
	}
}
void dfs(int u)
{
	for (int v : edge1[u])
	{
		if (v == parent[u]) continue;
		parent[v] = u;
		depth[v] = depth[u] + 1;
		dfs(v);
	}
}
void dfs1(int u)
{
	dp1[u] = {0, 1};
	for (int v : edge1[u])
	{
		if (v == parent[u]) continue;
		dfs1(v);
		pii p = {dp1[v].fi + 1, dp1[v].se};
		ckmax(diam, p.fi + dp1[u].fi);
		if (p.fi == dp1[u].fi)
		{
			dp1[u].se += p.se;
		}
		else if (p.fi > dp1[u].fi)
		{
			dp1[u] = p;
		}
	}
}
void dfs2(int u)
{
	int big = 0; ll num = 0, tot = 0;
	for (int v : edge1[u])
	{
		if (v == parent[u]) continue;
		dfs2(v);
	}
	for (int v : edge1[u])
	{
		if (v == parent[u]) continue;
		ckmax(big, dp1[v].fi + 1);
	}
	for (int v : edge1[u])
	{
		if (v == parent[u]) continue;
		if (dp1[v].fi + 1 == big)
		{
			tot += dp1[v].se;
		}
	}
	for (int v : edge1[u])
	{
		if (v == parent[u]) continue;
		if (dp1[v].fi + 1 + big == diam)
		{
			ans += dp1[v].se * (dp1[v].fi + 1 == big ? num : tot);
		}
		if (dp1[v].fi + 1 == big)
		{
			num += dp1[v].se;
		}
	}
	if (big == diam)
	{
		ans += num;
	}
}

int32_t main()
{
	ios_base::sync_with_stdio(0); cin.tie(0);
	// cout << fixed << setprecision(10);
	// cerr << fixed << setprecision(10);
	// if (fopen("file.in", "r"))
	// {
	// 	freopen ("file.in", "r", stdin);
	// 	freopen ("file.out", "w", stdout);
	// }
	cin >> N;
	FOR(i, 0, N) dsu[i] = i;
	FOR(i, 0, N)
	{
		int u, v;
		cin >> u >> v;
		u--; v--;
		edge[u].PB(v);
		edge[v].PB(u);
		if (!merge(u, v))
		{
			U = u; V = v;
			// DBG(U); DBG(V);
		}
	}
	FOR(i, 0, N) parent[i] = N;
	DFS(U);
	while(V != N)
	{
		cyc.PB(V);
		inside[V] = true;
		V = parent[V];
	}
	M = SZ(cyc);
	for (int u : cyc)
	{
		solve(u, -1);
		for (int v : nodes)
		{
			depth[v] = 0;
			parent[v] = N;
		}
		dfs(u);
		dfs1(u);
		dfs2(u);
		res.PB({diam, ans});
		diam = 0; ans = 0;
		nodes.clear();
		// cerr << u << ' ' << diam << ' ' << ans << endl;
	}
	multiset<int> s;
	FOR(j, 0, M / 2)
	{
		s.insert(j + dp[cyc[j]].fi);
		cerr << "insert " << j << endl;
	}
	FOR(i, 0, M)
	{
		int u = i;
		// cerr << "erase " << u << endl;
		s.erase(s.find(u + dp[cyc[u]].fi));
		u = (i + (M / 2)) % M;
		s.insert(u + dp[cyc[u]].fi);
		// cerr << "insert " << u << endl;
		ckmax(diam, -i + dp[cyc[i]].fi + *s.rbegin());
		// FOR(j, i + 1, i + (M / 2) + 1)
		// {
		// 	int v = cyc[j % M];
		// 	ckmax(diam, (-i + dp[u].fi) + (j + dp[v].fi));
		// }
	}
	// DBG(diam);
	FOR(i, 0, M)
	{
		int u = cyc[i];
		FOR(j, i + 1, i + (M / 2) + 1)
		{
			int v = cyc[j % M];
			if (j - i + (dp[u].fi + dp[v].fi) == diam)
			{
				// cerr << u << " -> " << v << endl;
				// cerr << M << ' ' << (j - i) * 2 << endl;
				ans += 1ll * dp[u].se * dp[v].se;
				// if ((j - i) * 2 == M)
				// {
				// 	ans += 1ll * dp[u].se * dp[v].se;
				// }
			}
		}
	}
	res.PB({diam, ans});
	// cerr << diam << ' ' << ans << endl;
	diam = 0; ans = 0;
	FOR(i, 0, SZ(res))
	{
		ckmax(diam, res[i].fi);
	}
	FOR(i, 0, SZ(res))
	{
		if (res[i].fi == diam)
		{
			ans += res[i].se;
		}
	}
	cout << ans << '\n';
	// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}
/* READ READ READ
* int overflow, maxn too small, special cases (n=1?, two distinct?), cin.tie() interactive
* reread the problem, try small cases
* note down possible sources of error as you go
* do smth instead of nothing
*/

• Subtask 1: 0 / 30
• Subtask 2: 0 / 20
• Subtask 3: 0 / 50