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 sys
from collections import defaultdict, Counter, deque
from itertools import accumulate, permutations, combinations
from operator import itemgetter
from bisect import bisect_left, bisect_right, bisect
from heapq import heappop, heappush
from fractions import gcd
from math import ceil, floor, sqrt, cos, sin, pi
from copy import deepcopy

# If you use recursive call, uncomment this code
#sys.setrecursionlimit(10**6)

def solve(N,D):
    if D[0]:
        return 0

    try:
        idx = D[1::].index(0)
        for d in D[idx+1::]:
            if d:
                return 0
    except:
        pass
    
    nums = Counter(D)
    nums = sorted(nums.items())
    #print(nums)
    ans = 1
    for i in range(len(nums)-1):
        ans *= nums[i][1]**nums[i+1][1]
        ans %= 998244353
    return ans

def main():
    N = int(input())
    D = list(map(int, input().split()))
    
    print(solve(N,D))

if __name__ == '__main__':
    main()