Language: C++

#include <bits/stdc++.h>

template <class T>
inline void read(T &x) {
	static char ch; 
	static bool opt; 
	while (!isdigit(ch = getchar()) && ch != '-'); 
	x = (opt = ch == '-') ? 0 : ch - '0'; 
	while (isdigit(ch = getchar()))
		x = x * 10 + ch - '0'; 
	if (opt)
		x = ~x + 1; 
}

template <class T>
inline void putint(T x) {
	static char buf[45], *tail = buf; 
	if (!x)
		putchar('0'); 
	else {
		if (x < 0)
			putchar('-'), x = ~x + 1; 
		for (; x; x /= 10) *++tail = x % 10 + '0'; 
		for (; tail != buf; --tail) putchar(*tail); 
	}
}

template <class T>
inline bool tense(T &x, const T &y) {
	return y < x ? x = y, true : false; 
}

template <class T>
inline bool relax(T &x, const T &y) {
	return x < y ? x = y, true : false; 
}

template <class T>
inline T getAbs(const T &x) {
	return x < 0 ? -x : x; 
}

typedef long long s64; 
typedef long double ld; 
typedef std::vector<int> vi; 
typedef std::pair<int, int> pii; 
#define mp(x, y) std::make_pair(x, y)

const int mod = 1e9 + 7; 

inline int qpow(int x, int y) {
	int res = 1; 
	for (; y; y >>= 1, x = 1LL * x * x % mod)
		if (y & 1) res = 1LL * res * x % mod; 
	return res; 
}

inline void add(int &x, const int &y) {
	if (x += y, x >= mod) x -= mod; 
}

const int MaxN = 1 << 18 | 5; 
const int MaxE = MaxN * 18 * 18 / 2 + 5; 

const int M = MaxE; 

int H, n, m; 
int p[MaxN], prod[MaxN], pinv[MaxN]; 

int ect; 
int adj[M], vX[MaxE], vY[MaxE], weight[MaxE], nxt[MaxE]; 

void insert(int x, int y, int val) {
	int u = (x * 993244853LL + y) % M; 

	for (int e = adj[u]; e; e = nxt[e])
		if (vX[e] == x && vY[e] == y) {
			add(weight[e], val); 
			return; 
		}
	
	nxt[++ect] = adj[u]; 
	adj[u] = ect; 

	vX[ect] = x, vY[ect] = y; 
	weight[ect] = val; 
}

int query(int x, int y) {
	int u = (x * 993244853LL + y) % M; 
	for (int e = adj[u]; e; e = nxt[e])
		if (vX[e] == x && vY[e] == y) {
			return weight[e]; 
		}
	return 0; 
}

int main() {
#ifdef orzczk
	freopen("a.in", "r", stdin); 
#endif

  	read(H); 
	n = 1 << H, m = (n + 1) >> 1; 

	pinv[0] = 1, prod[1] = pinv[1] = 1; 
	for (int i = 2; i < n; ++i) {
		prod[i] = 1LL * prod[i >> 1] * i % mod; 
		pinv[i] = qpow(1LL * prod[i] * prod[i >> 1] % mod, mod - 2); 
	}

	int ans = 0; 
	for (int i = m; i < n; ++i) {
      read(p[i]); 
      p[i] += m - 1; 
      
		for (int x = i; x > 1; x >>= 1) if (visA[x ^ 1])
			for (int y = p[i]; y > 1; y >>= 1) if (visB[y ^ 1]) {
				add(ans, 1LL * prod[i] * prod[p[i]] % mod * query(x ^ 1, y ^ 1) % mod); 
			}
		
		for (int x = i; x > 1; x >>= 1) {
          visA[x] = true; 
			for (int y = p[i]; y > 1; y >>= 1) {
              visB[y] = true; 
				insert(x, y, 1LL * pinv[x >> 1] * pinv[y >> 1] % mod * prod[i] % mod * prod[p[i]] % mod); 
			}
        }
	}

	std::cout << ans << '\n'; 

	return 0; 
}

Compiler output:
a.cc: In function 'int main()':
a.cc:117:53: error: 'visA' was not declared in this scope; did you mean 'vi'?
  117 |                 for (int x = i; x > 1; x >>= 1) if (visA[x ^ 1])
      |                                                     ^~~~
      |                                                     vi
a.cc:118:64: error: 'visB' was not declared in this scope; did you mean 'vi'?
  118 |                         for (int y = p[i]; y > 1; y >>= 1) if (visB[y ^ 1]) {
      |                                                                ^~~~
      |                                                                vi
a.cc:123:11: error: 'visA' was not declared in this scope; did you mean 'vi'?
  123 |           visA[x] = true;
      |           ^~~~
      |           vi
a.cc:125:15: error: 'visB' was not declared in this scope; did you mean 'vi'?
  125 |               visB[y] = true;
      |               ^~~~
      |               vi