Language: C++

#include "bits/stdc++.h"
#include<unordered_map>
#pragma warning(disable:4996)
using namespace std;
const int mod = 1000000007;
struct Mod {
public:
	int num;
	Mod() : num(0) { ; }
	Mod(long long int n) : num((n % mod + mod) % mod) { ; }
	Mod(int n) : num((n % mod + mod) % mod) { ; }
	operator int() { return num; }
};

Mod operator+(const Mod a, const Mod b) { return Mod((a.num + b.num) % mod); }
Mod operator+(const long long int a, const Mod b) { return Mod(a) + b; }
Mod operator++(Mod &a) { return a + Mod(1); }
Mod operator-(const Mod a, const Mod b) { return Mod((mod + a.num - b.num) % mod); }
Mod operator-(const long long int a, const Mod b) { return Mod(a) - b; }
Mod operator--(Mod &a) { return a - Mod(1); }
Mod operator*(const Mod a, const Mod b) { return Mod(((long long)a.num * b.num) % mod); }
Mod operator*(const long long int a, const Mod b) { return Mod(a)*b; }
Mod operator+=(Mod &a, const Mod b) { return a = a + b; }
Mod operator+=(long long int &a, const Mod b) { return a = a + b; }
Mod operator-=(Mod &a, const Mod b) { return a = a - b; }
Mod operator-=(long long int &a, const Mod b) { return a = a - b; }
Mod operator*=(Mod &a, const Mod b) { return a = a * b; }
Mod operator*=(long long int &a, const Mod b) { return a = a * b; }
Mod operator^(const Mod a, const int n) {
	if (n == 0) return Mod(1);
	Mod res = (a * a) ^ (n / 2);
	if (n % 2) res = res * a;
	return res;
}
Mod mod_pow(const Mod a, const int n) {
	if (n == 0) return Mod(1);
	Mod res = mod_pow((a * a), (n / 2));
	if (n % 2) res = res * a;
	return res;
}
Mod inv(const Mod a) { return a ^ (mod - 2); }
Mod operator/(const Mod a, const Mod b) {
	assert(b.num != 0);
	return a * inv(b);
}
Mod operator/(const long long int a, const Mod b) {
	assert(b.num != 0);
	return Mod(a) * inv(b);
}
Mod operator/=(Mod &a, const Mod b) {
	assert(b.num != 0);
	return a = a * inv(b);
}

#define MAX_MOD_N 1024000

Mod fact[MAX_MOD_N], factinv[MAX_MOD_N];
void init() {
	fact[0] = Mod(1); factinv[0] = 1;
	for (int i = 0; i < MAX_MOD_N - 1; ++i) {
		fact[i + 1] = fact[i] * Mod(i + 1);
		factinv[i + 1] = factinv[i] / Mod(i + 1);
	}
}
Mod comb(const int a, const int b) {
	return fact[a] * factinv[b] * factinv[a - b];
}
struct Node {
	int id;
	int paid;
	vector<int>chid;
	Node(int a) :chid() {
		id = a;
		paid = -1;
	}
};
vector<Node>nodes;
map<int, Mod>getans(const int nid) {
	if (nodes[nid].chid.size() == 0) {
		const map<int, Mod>mp{ 1,1 };
		return mp;
	}
	else if (nodes[nid].chid.size() == 1) {
		const map<int, Mod>mp(getans(nodes[nid].chid[0]));
		map<int, Mod>nmp;
		for (auto i : mp) {
			nmp[i.first + 1] = i.second;
		}
		return nmp;
	}
	else {
		map<int, Mod> now = getans(nodes[nid].chid[0]);
		for (int i = 1; i < nodes[nid].chid.size(); ++i) {
			const map<int, Mod>next = getans(nodes[nid].chid[i]);
			map<int, Mod>newmap;
			for (const auto j : now) {
				for (const auto k : next) {
					pair< int, Mod>l(j);
					pair< int, Mod>r(k);
					if (l.first < r.first) {
						swap(l, r);
					}
					assert(l.first >= r.first);
					for (int sum = l.first; sum <= l.first + r.first; ++sum) {
						const int kaburi = l.first + r.first - sum;
						const int kaburazu = sum - l.first;

						Mod ans = comb(l.first, kaburi);
						ans *= comb(l.first + kaburazu, kaburazu);
						ans *= l.second*r.second;
						newmap[sum] += ans;
					}

				}
			}
			now = newmap;
		}
		map<int, Mod>nmp;
		for (auto i : now) {
			nmp[i.first + 1] = i.second;
		}
		return nmp;
	}
}
int main() {
	init();
	int N; cin >> N;
	for (int i = 0; i < N; ++i) {
		nodes.push_back(Node(i));
	}
	for (int i = 0; i < N - 1; ++i) {
		int a, b; cin >> a >> b;
		nodes[a].chid.push_back(b);
		nodes[b].paid = a;
	}
	int root;
	for (int i = 0; i < N; ++i) {
		if (nodes[i].paid == -1) {
			root = i;
		}
	}
	map<int, Mod>ans(getans(a));
	Mod sum = 0;
	for (auto i : ans) {
		sum += i.second;
	}
	cout << sum << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:142:33: error: 'a' was not declared in this scope
  142 |         map<int, Mod>ans(getans(a));
      |                                 ^
In file included from /usr/include/c++/14/map:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_map.h: In instantiation of 'std::map<_Key, _Tp, _Compare, _Alloc>::map(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = Mod; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, Mod> >]':
a.cc:80:30:   required from here
   80 |                 const map<int, Mod>mp{ 1,1 };
      |                                            ^
/usr/include/c++/14/bits/stl_map.h:287:38: error: no matching function for call to 'std::_Rb_tree<int, std::pair<const int, Mod>, std::_Select1st<std::pair<const int, Mod> >, std::less<int>, std::allocator<std::pair<const int, Mod> > >::_M_insert_range_unique(int&, int&)'
  287 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/map:62:
/usr/include/c++/14/bits/stl_tree.h:1096:9: note: candidate: 'template<class _InputIterator> std::__enable_if_t<((bool)std::is_same<_Val, typename std::iterator_traits<_InputIterator>::value_type>::value)> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_range_unique(_InputIterator, _InputIterator) [with _Key = int; _Val = std::pair<const int, Mod>; _KeyOfValue = std::_Select1st<std::pair<const int, Mod> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, Mod> >]'
 1096 |         _M_insert_range_unique(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:1096:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_tree.h: In substitution of 'template<class _InputIterator> std::__enable_if_t<((bool)std::is_same<std::pair<const int, Mod>, typename std::iterator_traits< <template-parameter-1-1> >::value_type>::value), void> std::_Rb_tree<int, std::pair<const int, Mod>, std::_Select1st<std::pair<const int, Mod> >, std::less<int>, std::allocator<std::pair<const int, Mod> > >::_M_insert_range_unique(_InputIterator, _InputIterator) [with _InputIterator = int]':
/usr/include/c++/14/bits/stl_map.h:287:31:   required from 'std::map<_Key, _Tp, _Compare, _Alloc>::map(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = Mod; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, Mod> >]'
  287 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
a.cc:80:30:   required from here
   80 |                 const map<int, Mod>mp{ 1,1 };
      |                                            ^
/usr/include/c++/14/bits/stl_tree.h:1095:58: error: no type named 'value_type' in 'struct std::iterator_traits<int>'
 1095 |         __enable_if_t<__same_value_type<_InputIterator>::value>
      |                                                          ^~~~~
/usr/include/c++/14/bits/stl_map.h: In instantiation of 'std::map<_Key, _Tp, _Compare, _Alloc>::map(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = Mod; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, Mod> >]':
a.cc:80:30:   required from here
   80 |                 const map<int, Mod>mp{ 1,1 };
      |                                            ^
/usr/include/c++/14/bits/stl_tree.h:1105:9: note: candidate: 'template<class _InputIterator> std::__enable_if_t<((bool)(! std::is_same<_Val, typename std::iterator_traits<_InputIterator>::value_type>::value))> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_range_unique(_InputIterator, _InputIterator) [with _Key = int; _Val = std::pair<const int, Mod>; _KeyOfValue = std::_Select1st<std::pair<const int, Mod> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, Mod> >]'
 1105 |         _M_insert_range_unique(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:1105:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_tree.h: In substitution of 'template<class _InputIterator> std::__enable_if_t<((bool)(! std::is_same<std::pair<const int, Mod>, typename std::iterator_traits< <template-parameter-1-1> >::value_type>::value)), void> std::_Rb_tree<int, std::pair<const int, Mod>, std::_Select1st<std::pair<const int, Mod> >, std::less<int>, std::allocator<std::pair<const int, Mod> > >::_M_insert_range_unique(_InputIterator, _InputIterator) [with _InputIterator = int]':
/usr/include/c++/14/bits/stl_map.h:287:31:   required from 'std::map<_Key, _Tp, _Compare, _Alloc>::map(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = Mod; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, Mod> >]'
  287 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
a.cc:80:30:   required from here
   80 |                 const map<int, Mod>mp{ 1,1 };
      |                                            ^
/usr/include/c++/14/bits/stl_tree.h:1104:59: error: no type named 'value_type' in 'struct std::iterator_traits<int>'
 1104 |         __enable_if_t<!__same_value_type<_InputIterator>::value>
      |                                                           ^~~~~