python - list index out of range - CodingBat Problem - Has22

Question

Here's the problem.

This is part of the List-2

Medium python list problems -- 1 loop.

• Given an array of ints, return True if the array contains a 2 next to a 2 somewhere.

  has22([1, 2, 2]) → True
  has22([1, 2, 1, 2]) → False
  has22([2, 1, 2]) → False

---

I was getting the error "list index is out of range" at first

I know where I was going wrong on line 4 of the original problem because once it is at the last number in the list it cannot add one anymore.

I have provided my original code below. The first code block was when I was getting the error "index out of range". The second solution works but I am wondering if there is a cleaner way of writing it.

Also on CodingBat when I run my solution it says "Other Tests" Failed at the bottom but no example I'm not sure what that means.

Thanks

Here's my code block - FIRST TRY:

def has22(nums):
    for i in range(len(nums)):
        first = nums[i]
        second = nums[i+1]
    if first == second:
    return True

MY SOLUTION:

def has22(nums):
    size = len(nums)
    for i in range(len(nums)):
        first = nums[i]
        if size >= i+2:
            second = nums[i+1]
        if first == second:
            return True
    return False

question from:https://stackoverflow.com/questions/65852959/list-index-out-of-range-codingbat-problem-has22

Answer 1

So if the question is whether the solution can be written cleaner, I think something like this should work:

def has22(nums):
    return (2, 2) in zip(num, num[1:])

and it looks pretty clean.

A little bit of explanation - zip creates pairs of values from 2 lists, so I just slice the input list into 2, where in the second list I omit the first element. Then I simply check whether tuple 2, 2 exists in the zipped pairs.

BTW I just noticed a bug in your solution - it returns True for input e.g. [2, 1] (basically any input, where 2 is second to last. So to fix this bug, and preserve the original "idea" of your solution, you could write it like this:

def has22(nums):
   for i, el in enumerate(nums):
       if el == 2 and i + 1 < len(nums) and nums[i + 1] == 2:
           return True
   return False

enumerate is the preferred way of iterating through a list with indices.