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.
example:
```
[2,10,9,3] is Nice array because
2=3-1
10=9+1
3=2+1
9=10-1
```
Write a function named `isNice`/`IsNice` that returns `true` if its array argument is a Nice array, else `false`. You should also return `false` if `input` array has `no` elements.
def is_nice(arr):
    if not arr: return False
    
    for x in arr:
        if x-1 not in arr and x+1 not in arr:       
            return False
    return True
def is_nice(arr):
    if not arr: return False
    
    for x in arr:
        if x-1 not in arr and x+1 not in arr:       
            return False
    return True