Submission #45791900

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Source Code Expand

// LUOGU_RID: 125557934
#include <bits/stdc++.h>
#define debug cerr << "[" << __LINE__ << "] "
#define SZ(x) (int) x.size() - 1
#define all(x) x.begin(), x.end()
#define ms(x, y) memset(x, y, sizeof x)
#define F(i, x, y) for (int i = (x); i <= (y); i++)
#define DF(i, x, y) for (int i = (x); i >= (y); i--)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
template <typename T> inline void chkmax(T& x, T y) { x = max(x, y); }
template <typename T> inline void chkmin(T& x, T y) { x = min(x, y); }
template <typename T> inline void read(T &x) {
	x = 0; int f = 1; char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
	for (; isdigit(c); c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
	x *= f;
}
const int N = 2e5 + 10, MOD = 998244353;
int n;
vector <int> v[N];
int dep[N], ans, inv[N], s[N];
inline void binom(int x) {
	inv[1] = 1;
	F(i, 2, x) inv[i] = (ll) (MOD - MOD / i) * inv[MOD % i] % MOD;
	F(i, 1, x) s[i] = (s[i - 1] + inv[i]) % MOD;
}
inline void add(int &x, ll y) { x = (x + y) % MOD; }
void dfs(int x, int fa) {
	dep[x] = dep[fa] + 1;
	add(ans, s[dep[x]]);
	for (int i: v[x])
		if (i != fa) dfs(i, x);
}
signed main() {
	read(n);
	binom(n);
	F(i, 2, n) {
		int x; read(x);
		v[x].push_back(i);
	}
	dfs(1, 0);
	cout << ans;
	return 0;
}

Submission Info

Judge Result