Language: C

#if 0
cat <<EOF >mistaken-paste
#endif
// thanks for @rsk0315_h4x

#pragma GCC diagnostic ignored "-Wincompatible-pointer-types"
#define _USE_MATH_DEFINES

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <math.h>
#include <time.h>

#define BIG 2000000007
#define VERYBIG 2000000000000007LL

#define MOD 1000000007
#define FOD  998244353
typedef uint64_t ull;
typedef  int64_t sll;

#define N_MAX 1000000

#ifdef __cplusplus
#include <queue>
#include <stack>
#include <tuple>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <functional>
#include <array>

using std::queue;
using std::priority_queue;
using std::stack;
using std::tuple;
using std::set;
using std::map;
using std::vector;
using std::greater;
using std::pair;
using std::string;
using std::get;

template <typename T, typename U>
pair<T, U> operator+(pair<T, U> l, pair<T, U> r) {
	return pair<T, U>(l.first + r.first, l.second + r.second);
}

#endif

typedef struct {
	int32_t a;
	int32_t b;
} hw;

typedef struct {
	sll a;
	sll b;
} hwll;

typedef struct {
	sll a;
	sll b;
	sll c;
} hwllc;

typedef struct {
	hwll a;
	hwll b;
} linell;

ull n, m;
ull h, w;
ull k;
ull q;
sll va, vb, vc, vd, ve, vf;
ull ua, ub, uc, ud, ue, uf;
long double vra, vrb, vrc;
double vda, vdb, vdc;
char ch, dh;

ull umin (ull x, ull y) {
	return (x < y) ? x : y;
}

ull umax (ull x, ull y) {
	return (x > y) ? x : y;
}

sll smin (sll x, sll y) {
	return (x < y) ? x : y;
}

sll smax (sll x, sll y) {
	return (x > y) ? x : y;
}

ull gcd (ull x, ull y) {
	if (x < y) {
		return gcd(y, x);
	} else if (y == 0) {
		return x;
	} else {
		return gcd(y, x % y);
	}
}

ull bitpow (ull a, ull x, ull modulo) {
	ull result = 1;
	while (x) {
		if (x & 1) {
			result *= a;
			result %= modulo;
		}
		x /= 2;
		a = (a * a) % modulo;
	}
	return result;
}

ull divide (ull a, ull b, ull modulo) {
	return (a * bitpow(b, modulo - 2, modulo)) % modulo;
}

ull udiff (ull a, ull b) {
	if (a >= b) {
		return a - b;
	} else {
		return b - a;
	}
}

sll sdiff (sll a, sll b) {
	if (a >= b) {
		return a - b;
	} else {
		return b - a;
	}
}

int bitcount (ull n) {
	int result = 0;
	while (n) {
		if (n & 1) result++;
		n /= 2;
	}
	return result;
}

#define BEGCMP(NAME) int32_t NAME (const void *left, const void *right)
#define DEFLR(TYPE) TYPE l=*(TYPE*)left,r=*(TYPE*)right
#define CMPRET(L, R) if((L)<(R))return-1;if((L)>(R))return+1

// int32_t pullcomp (const void *left, const void *right) {
// 	ull l = *(ull*)left;
// 	ull r = *(ull*)right;
// 	if (l < r) {
// 		return -1;
// 	}
// 	if (l > r) {
// 		return +1;
// 	}
// 	return 0;
// }
BEGCMP(pullcomp){
	DEFLR(ull);
	CMPRET(l, r);
	return 0;
}
BEGCMP(prevcomp){
	DEFLR(ull);
	CMPRET(r, l);
	return 0;
}
BEGCMP(psllcomp){
	DEFLR(sll);
	CMPRET(l, r);
	return 0;
}
BEGCMP(pcharcomp){
	DEFLR(char);
	CMPRET(l, r);
	return 0;
}
BEGCMP(pdoublecomp){
	DEFLR(double);
	CMPRET(l, r);
	return 0;
}

int32_t pstrcomp (const void *left, const void *right) {
	char* l = *(char**)left;
	char* r = *(char**)right;

	return strcmp(l, r);
}

BEGCMP(phwllABcomp){
	DEFLR(hwll);
	CMPRET(l.a, r.a);
	CMPRET(l.b, r.b);
	return 0;
}
BEGCMP(phwllREVcomp){
	DEFLR(hwll);
	CMPRET(l.b, r.b);
	CMPRET(l.a, r.a);
	return 0;
}
BEGCMP(ptriplecomp){
	DEFLR(hwllc);
	CMPRET(l.a, r.a);
	CMPRET(l.b, r.b);
	CMPRET(l.c, r.c);
	return 0;
}
BEGCMP(ptripleREVcomp){
	DEFLR(hwllc);
	CMPRET(l.b, r.b);
	CMPRET(l.a, r.a);
	CMPRET(l.c, r.c);
	return 0;
}

int32_t pquadcomp (const void *left, const void *right) {
	linell l = *(linell*)left;
	linell r = *(linell*)right;

	sll ac = phwllABcomp(&(l.a), &(r.a));
	if (ac) return ac;
	sll bc = phwllABcomp(&(l.b), &(r.b));
	if (bc) return bc;

	return 0;
}

bool isinrange (sll left, sll x, sll right) {
	return (left <= x && x <= right);
}

bool isinrange_soft (sll left, sll x, sll right) {
	return (left <= x && x <= right) || (left >= x && x >= right);
}

sll a[N_MAX + 5];
// ull a[N_MAX];
// sll a[3001][3001];
sll b[N_MAX + 5];
// sll b[3001][3001];
sll c[N_MAX + 5];
sll d[N_MAX + 5];
// sll e[N_MAX];
char s[N_MAX + 1];
// char s[3010][3010];
char t[N_MAX + 1];
// char t[3010][3010];
char u[N_MAX + 1];
hwll xy[N_MAX];
hwllc tup[N_MAX];
sll table[3000][3000];
// here we go

vector<sll> g[N_MAX];

ull depnum[N_MAX];
typedef tuple<sll, sll, sll> T;
typedef pair<sll, vector<T>> sT;

T mul (T l, T r) {
	T x(0LL, 0LL, 0LL);

	get<0>(x) += get<0>(l) * get<0>(r) % MOD;
	get<1>(x) += get<0>(l) * get<1>(r) % MOD;
	get<0>(x) += get<0>(l) * get<2>(r) % MOD;
	get<1>(x) += get<1>(l) * get<0>(r) % MOD;
	get<2>(x) += get<1>(l) * get<1>(r) % MOD;
	get<1>(x) += get<1>(l) * get<2>(r) % MOD;
	get<2>(x) += get<2>(l) * get<0>(r) % MOD;
	get<2>(x) += get<2>(l) * get<1>(r) % MOD;
	get<2>(x) += get<2>(l) * get<2>(r) % MOD;

	get<0>(x) %= MOD;
	get<1>(x) %= MOD;
	get<2>(x) %= MOD;

	return x;
}

vector<T> dfs (ull v, ull d) {
	depnum[d]++;

	vector<T> r;

	priority_queue<sT, vector<sT> > q;
	for (sll u : g[v]) {
		vector<T> t = dfs(u, d + 1);
		q.push(sT(t.size(), t));
	}

	if (!q.empty()) {
		r = q.top().second;
		q.pop();

		bool isfirst = true;
		while (!q.empty()) {
			vector<T> t = q.top().second;
			q.pop();

			for (sll i = t.size() - 1; i >= 0; i--) {
				T left = r[r.size() - 1 - i], right = t[t.size() - 1 - i];
				if (isfirst) {
					get<0>(left) = (get<0>(left) + get<2>(left)) % MOD;
					get<2>(left) = 0LL;
				}

				// printf("%lld.%lld,%lld * %lld,%lld,%lld -> ", 
				// 	get<0>(left), get<1>(left), get<2>(left), get<0>(right), get<1>(right), get<2>(right));

				r[r.size() - 1 - i] = mul(left, right);
				// printf("%lld.%lld,%lld\n", 
					// get<0>(r[r.size() - 1 - i]), get<1>(r[r.size() - 1 - i]), get<2>(r[r.size() - 1 - i]));
			}

			isfirst = false;
		}
	}

	r.push_back(T(1LL, 1LL, 0LL));
	return r;
}

ull solve () {
	sll i, j, ki, li;
	// ull result = 0;
	sll result = 0;
	double dresult = 0;
	// ull maybe = 0;
	sll maybe = 0;
	// ull sum = 0;
	sll sum = 0;
	sll item;
	ull *dpcell;

	n++;

	for (i = 1; i < n; i++) {
		g[a[i]].push_back(i);
	}
	vector<T> t = dfs(0, 0);
	result = 0;
	for (sll i = t.size() - 1; i >= 0; i--) {
		T x = t[t.size() - 1 - i];

		result = (result + (get<1>(x) * bitpow(2, n - depnum[i], MOD) % MOD)) % MOD;
	}


	printf("%lld\n", result);
	// printf("%.15lf\n", dresult);
	// puts(s);

	return 0;

	success:
	// puts("YES");
	// puts("Yes");
	printf("%llu\n", result);
	// puts("0");
	// puts("Yay!");
	return 0;

	fail:
	// puts("NO");
	// puts("No");
	// puts("0");
	// puts("-1");
	// puts("-1 -1 -1");
	puts("Impossible");
	return 1;
}

int32_t main (void) {
	int32_t i, j;
	int32_t x, y;



	// scanf("%llu%llu", &h, &w);
	scanf("%llu", &n, &m);
	// scanf("%llu", &k, &n, &m);
	// scanf("%llu%llu", &h, &w);
	// scanf("%llu", &q);
	// scanf("%s", s);
	// scanf("%lld%lld%lld%lld", &va, &vb, &vc, &vd);
	// scanf("%llu%llu%llu", &ua, &ub, &uc, &ud);
	// scanf("%s", t);
	// scanf("%d", &n);
	for (i = 1; i <= n; i++) {
		// scanf("%lld%lld", &xy[i].a, &xy[i].b);
		// scanf("%lld%lld%lld", &tup[i].a, &tup[i].b, &tup[i].c);
		scanf("%lld", &a[i]);
		// scanf("%lld", &b[i]);
		// scanf("%lld", &c[i]);
		// scanf("%lld", &d[i]);
		// a[i]--;
		// b[i]--;
		// c[i]--;
		// d[i]--;
		// tup[i].a--;
		// tup[i].b--;
	}
	// scanf("%llu", &m, &k);
	// scanf("%llu", &q);
	// scanf("%s", s);
	// for (i = 0; i < n; i++) {
	// 	scanf("%lld", &b[i]);
	// 	// b[i]--;
	// }
	// scanf("%llu", &q);

	// for (i = 0; i < h; i++) {
	// 	for (j = 0; j < w; j++) {
	// 		scanf("%llu", &table[i][j]);
	// 	}
	// }
	// for (i = 0; i < h; i++) {
	// 	scanf("%s", &s[i]);
	// }

	solve();

	return 0;
}


Compiler output:
main.c:269:7: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
  269 | vector<sll> g[N_MAX];
      |       ^
main.c:272:14: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
  272 | typedef tuple<sll, sll, sll> T;
      |              ^
main.c:273:13: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
  273 | typedef pair<sll, vector<T>> sT;
      |             ^
main.c:275:1: error: unknown type name 'T'
  275 | T mul (T l, T r) {
      | ^
main.c:275:8: error: unknown type name 'T'
  275 | T mul (T l, T r) {
      |        ^
main.c:275:13: error: unknown type name 'T'
  275 | T mul (T l, T r) {
      |             ^
main.c:295:7: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
  295 | vector<T> dfs (ull v, ull d) {
      |       ^
main.c: In function 'solve':
main.c:353:17: error: 'g' undeclared (first use in this function)
  353 |                 g[a[i]].push_back(i);
      |                 ^
main.c:353:17: note: each undeclared identifier is reported only once for each function it appears in
main.c:355:9: error: 'vector' undeclared (first use in this function)
  355 |         vector<T> t = dfs(0, 0);
      |         ^~~~~~
main.c:355:16: error: 'T' undeclared (first use in this function)
  355 |         vector<T> t = dfs(0, 0);
      |                ^
main.c:355:23: error: implicit declaration of function 'dfs'; did you mean 'ffs'? [-Wimplicit-function-declaration]
  355 |         vector<T> t = dfs(0, 0);
      |                       ^~~
      |                       ffs
main.c:357:23: error: request for member 'size' in something not a structure or union
  357 |         for (sll i = t.size() - 1; i >= 0; i--) {
      |                       ^
main.c:358:18: error: expected ';' before 'x'
  358 |                 T x = t[t.size() - 1 - i];
      |                  ^~
      |                  ;
main.c:360:37: error: 'get' undeclared (first use in this function); did you mean 'getw'?
  360 |                 result = (result + (get<1>(x) * bitpow(2, n - depnum[i], MOD) % MOD)) % MOD;
      |                                     ^~~
      |                                     getw
main.c:360:44: error: 'x' undeclared (first use in this function)
  360 |                 result = (result + (get<1>(x) * bitpow(2, n - depnum[i], MOD) % MOD)) % MOD;
      |                                            ^