scratch paper

find_sum.py

import unittest

def has_pair_with_sum(a_list, target):
    if len(a_list) < 2:
        return False

    i, j = 0, len(a_list) - 1

    while i < j:
        min_value = a_list[i]
        max_value = a_list[j]

        tmp_sum = min_value + max_value

        if tmp_sum == target:
            return True
        elif tmp_sum < target:
            i += 1
        else: # tmp_sum > target:
            j -= 1

    return False

class FindTargetSum(unittest.TestCase):
    def test(self):
        l1 = [1, 3, 5, 8, 12, 13, 22]
        self.assertEqual(has_pair_with_sum(l1, 16), True)
        self.assertEqual(has_pair_with_sum(l1, 19), False)

    def test_another(self):
        l2 = [1, 3, 5]
        self.assertEqual(has_pair_with_sum(l2, 6), True)
        self.assertEqual(has_pair_with_sum(l2, 2), False)

if __name__ == '__main__':
    unittest.main()