How to find all ordered pairs of elements in array of integers whose sum lies in a given range of value

Question

Given an array of integers find the number of all ordered pairs of elements in the array whose sum lies in a given range [a,b]

Here is an O(n^2) solution for the same <

Answer 1

Rather than using the relational operators, we can simply check if the sum of array elements i and j are in the specified range.

def get_numOfPairs(array, start, stop):
    num_of_pairs = 0
    array_length = len(array)

    for i in range(array_length):
        for j in range(i+1, array_length):
            if sum([array[i], array[j]]) in range(start, stop):
                num_of_pairs += 1

    return num_of_pairs