A Common-Sense Guide to Data Structures and Algorithms in Python, Volume 1

A Practical Example

Suppose you’re writing a Python application, and somewhere in your code you find that you need to get the intersection between two arrays. The intersection is a list of all the values that occur in both of the arrays. For example, if you have the arrays [3, 1, 4, 2] and [4, 5, 3, 6], the intersection would be a third array [3, 4] since both of those values are common to the two arrays.

Here’s one possible implementation:

def intersection(first_array, second_array):
    result = []

    for i in first_array:
        for j in second_array:
            if i == j:
                result.append(i)

    return result

Here, we’re running nested loops. In the outer loop, we iterate over each value in the first array. As we point to each value in ...