Two_Number_Sum.py

# https://www.algoexpert.io/questions/Two%20Number%20Sum

# Solution 1 starts
# O(n^2) time | O(1) space
def twoNumberSum(array, targetSum):
    result_list = []
    for i in range(0, len(array) - 1):
        first_number = array[i]
        for j in range(i + 1, len(array)):
            second_number = array[j]
            sum = first_number + second_number
            if sum == targetSum:
                result_list.append(first_number)
                result_list.append(second_number)

    return sorted(result_list)
# Solution 1 ends

# Solution 2 starts
# O(n) time | O(n) space
def twoNumberSum2(array, targetSum):
    result_list = []
    for i in range(0, len(array) - 1):
        first_number = array[i]
        second_nsumber_expected = targetSum - first_number
        secondary_array = array[i + 1:len(array)]
        if second_nsumber_expected in secondary_array:
            result_list.append(first_number)
            result_list.append(second_nsumber_expected)

    return sorted(result_list)
# Solution 2 ends

# Solution 3 starts
# O(nlogn) time | O(1) space
def twoNumberSum3(array, targetSum):
    array.sort()
    left = 0
    right = len(array) - 1
    while left < right:
        current_sum = array[left] + array[right]
        if current_sum == targetSum:
            return [array[left], array[right]]
        elif current_sum < targetSum:
            left += 1
        elif current_sum > targetSum:
            right -= 1

    return []
# Solution 3 ends


print(twoNumberSum([5, 3, -4, 8, 11, 1, -1, 6], 10))