Find_the_first_non_consecutive_number.md

CodeWars Python Solutions

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Find the first non-consecutive number

Your task is to find the first element of an array that is not consecutive.

By not consecutive we mean not exactly 1 larger than the previous element of the array.

E.g. If we have an array [1,2,3,4,6,7,8] then 1 then 2 then 3 then 4 are all consecutive but 6 is not, so that's the first non-consecutive number.

If the whole array is consecutive then return null².

The array will always have at least 2 elements¹ and all elements will be numbers. The numbers will also all be unique and in ascending order. The numbers could be positive or negative and the first non-consecutive could be either too!

If you like this Kata, maybe try this one next: https://www.codewars.com/kata/represent-array-of-numbers-as-ranges

¹ Can you write a solution that will return null² for both [] and [ x ] though? ( This is not tested, but you can write your own example test. )

² Swift, Ruby and Crystal: nil
Haskell: Nothing
Python: None
Julia: nothing

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Given Code

def first_non_consecutive(arr):
    pass

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Solution

def first_non_consecutive(arr):
    i = 1
    for x in arr:
        if i < len(arr) and arr[i] - arr[i-1] != 1:
            return arr[i]
        i += 1
    return None

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