07_two_sum.py

"""
30 min

Write a function that, when passed a list and a target sum, returns, efficiently
with respect to time used, two distinct zero-based indices of any two of the
numbers, whose sum is equal to the target sum. If there are no two numbers,
the function should return None.

For example, find_two_sum([3, 1, 5, 7, 5, 9], 10) should return a single tuple
containing any of the following pairs of indices:

* 0 and 3 (or 3 and 0) as 3 + 7 = 10
* 1 and 5 (or 5 and 1) as 1 + 9 = 10
* 2 and 4 (or 4 and 2) as 5 + 5 = 10


def find_two_sum(numbers, target_sum):
    # :param numbers: (list of ints) The list of numbers.
    # :param target_sum: (int) The required target sum.
    # :returns: (a tuple of 2 ints) The indices of the two elements whose sum is equal to target_sum
    return None

print(find_two_sum([3, 1, 5, 7, 5, 9], 10))
"""


def find_two_sum(numbers, target_sum):
    """
    :param numbers: (list of ints) The list of numbers.
    :param target_sum: (int) The required target sum.
    :returns: (a tuple of 2 ints) The indices of the two elements whose sum is equal to target_sum
    """
    taken = {}
    for i, num in enumerate(numbers):
        diff = target_sum - num
        if diff in taken:
            return i, taken[diff]
        taken[num] = i
    return None


print(find_two_sum([3, 1, 5, 7, 5, 9], 10))