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)

CONST_DIVSOR = 998244353
N = int(input())
Ds = list(map(int, input().strip().split()))
counter = [0]*N
for D in Ds:
    counter[D] += 1
total = 0
cnt = 0
prenumi = 0
for i in range(N):
    if i == 0:
        if counter[i] == 1:
            total = 1
            prenumi = 1
            cnt = 1
        else:
            break
    else:
        numi = counter[i]
        if numi != 0:
            case = 1
            for j in range(numi):
                case = (case * prenumi) % CONST_DIVSOR
            total = (total * case) % CONST_DIVSOR
            prenumi = numi
            cnt += numi
        else:
            total = 0
            break
    # print(i,total,prenumi,cnt)
    if cnt >= N:
        break
 
print(total % CONST_DIVSOR)