Problem:
Score : 300 points

Problem Statement

Given is an integer sequence D_1,...,D_N of N elements. Find the number, modulo 998244353, of trees with N vertices numbered 1 to N that satisfy the following condition:

For every integer i from 1 to N, the distance between Vertex 1 and Vertex i is D_i.

Notes

A tree of N vertices is a connected undirected graph with N vertices and N-1 edges, and the distance between two vertices are the number of edges in the shortest path between them.

Two trees are considered different if and only if there are two vertices x and y such that there is an edge between x and y in one of those trees and not in the other.

Constraints

1 \leq N \leq 10^5

0 \leq D_i \leq N-1

Input

Input is given from Standard Input in the following format:

N
D_1 D_2 ... D_N

Output

Print the answer.

Sample Input 1

4
0 1 1 2

Sample Output 1

2

For example, a tree with edges (1,2), (1,3), and (2,4) satisfies the condition.

Sample Input 2

4
1 1 1 1

Sample Output 2

0

Sample Input 3

7
0 3 2 1 2 2 1

Sample Output 3

24

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

import collections


def mod_pow(a, n, mod):
    result = 1
    a_n = a
    while n > 0:
        if n & 1:
            result = result * a_n % mod
        a_n = a_n * a_n % mod
        n >>= 1
    return result


def main(n, d):
    MOD = 998244353
    counter = collections.Counter(d)
    if counter[0] != 1:
        return 0
    if 0 in counter.values():
        return 0
    pows = [mod_pow(a=counter[i - 1] % MOD, n=counter[i] % MOD, mod=MOD) for i
            in
            range(1, max(counter.keys()) + 1)]
    patterns = 1
    for p in pows:
        patterns *= p
        patterns %= MOD
    return patterns


if __name__ == '__main__':
    N = int(input())
    D = list(map(int, input().split()))
    print(main(n=N, d=D))