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Algorithms for Coding Interviews in Python

Solution: Find Two Numbers That Add Up to "n"

This review provides a detailed analysis of the different ways to solve the previous challenge.

We'll cover the following...

Solution #1: brute force

Python 3.5
def find_sum(lst, n):
    """
    Function to find two number that add up to n
    :param lst: A list of integers
    :param n: The integer number n
    """
    for i in range(len(lst)):
        for j in range(len(lst)):
            if lst[i] + lst[j] == n and i != j:
                return [lst[i], lst[j]]
# Driver code to test above
if __name__ == '__main__':
    
    print(find_sum([1, 2, 3, 4], 5))

Explanation

This is the most time-intensive, but intuitive solution. Traverse the whole list and for each element in the list, check if any two elements add up to the given number n. So, use a nested for loop and iterate over the entire list for each element.

Time complexity

Since we iterate over the entire list of nn elements, the time complexity is O(n2)O(n^2) ...