You will get an array of numbers. 

Every preceding number is smaller than the one following it.

Some numbers will be missing, for instance:
```
[-3,-2,1,5] //missing numbers are: -1,0,2,3,4
```
Your task is to return an array of those missing numbers:
```
[-1,0,2,3,4]
```

Difficulty: introductory

Starter code:

def find_missing_numbers(arr):
	

Solutions:
def find_missing_numbers(arr):
    if not arr:
        return []
    return sorted(set(range(arr[0] + 1, arr[-1])).difference(arr))


def find_missing_numbers(arr):
    return [x for x in range(arr[0], arr[-1]+1) if x not in arr] if arr else []

def find_missing_numbers(arr):
    return [n for n in range(arr[0], arr[-1]) if n not in arr] if arr else []

def find_missing_numbers(arr):
    return [x for x in range(arr[0], arr[-1]) if x not in arr] if arr else []

import itertools


def find_missing_numbers(arr):
    return list(itertools.chain.from_iterable(
        range(a+1, b)
        for a, b in zip(arr, arr[1:])
    ))

def find_missing_numbers(arr):
    if not arr: return arr
    out,it = [],iter(arr)
    ref    = next(it)
    for v in range(arr[0],arr[-1]):
        if v==ref: ref = next(it)
        else:      out.append(v)
    return out

def find_missing_numbers(arr):
    if len(arr) < 2:
        return []
    return sorted(set(list(range(min(arr), max(arr)))) - set(arr))

def find_missing_numbers(arr):
    if len(arr):
        return [i for i in range(arr[0],arr[-1]) if i not in arr]
    else :
        return []

def find_missing_numbers(arr):
    try:
        return [i for i in range(arr[0],arr[len(arr)-1]) if i not in arr]
    except IndexError:
        return []