Kata

A Nice array is defined to be an array where for every value n in the array, there is also an element n - 1 or n + 1 in the array.

examples:

[2, 10, 9, 3] is a nice array because

 2 =  3 - 1
10 =  9 + 1
 3 =  2 + 1
 9 = 10 - 1

[4, 2, 3] is a nice array because

4 = 3 + 1
2 = 3 - 1
3 = 2 + 1 (or 3 = 4 - 1)

[4, 2, 1] is a not a nice array because

for n = 4, there is neither n - 1 = 3 nor n + 1 = 5

Write a function named isNice/IsNice that returns true if its array argument is a Nice array, else false. An empty array is not considered nice.