Find the closest two values in an array where the difference is at least x

Question

Task: Given an unsorted array, how do I find the closest two values such that their absolute difference is at least x (return -1 if there is no two elements with this difference in the array)?

My approach: I tried using a sliding window approach:

• I start the first pointer at index 0 and the second pointer at index 1.
• I increment index 1 until I get the difference between the array elements at the first and second indexes are at least x.
• After that, I start incrementing the first index until the second index, keeping track of any values in between that are small enough to also match the difference of at least x.
• I do this until the second pointer makes it to the end of the array.

Here's my code with an example:

length = 6
x = 5
arr = [1, 1, 4, 3, 7, 5]

smallestRange = float('inf')
first = 0
second = 1

while (second < length):
    
    # Keep going until the proper difference is found
    while (second < length and abs(arr[first] - arr[second]) < x):
        second += 1
    
    # No matches are found
    if (second == length):
        break

    # Let first catch up to second
    minVal = first
    while (first != second):
        if (arr[first] <= arr[minVal] and abs(arr[first] - arr[second]) >= x):
            minVal = first
        first += 1
    
    if (minVal != second):
        if (second - minVal < smallestRange):
            smallestRange = second - minVal
    
    second += 1

if (smallestRange == float('inf')):
    smallestRange = -1
print(smallestRange)

Problem: This isn't covering all of the possible cases. For example, if the first element doesn't have any absolute differences with any of the other elements, my second pointer will just go straight to the end and my code just returns -1. I've also tried checking other input arrays by hand and sometimes it doesn't work. Could I get any pointers on how to fix this?

The example should result in printing 3 since 1 and 7 would be the closest pair that has a difference of at least 5.