LeetCode 167 - Two Sum II - 2023.10.08 solution

class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        """
        [2,7,11,15], target = 18
        Step 1: 17, we need more, so step in from the left
        Step 2: 22, we need less, so step in from the right

        Proposed solution: We start with the two pointers at the ends and
        step inwards based on whether the current sum is greater or less
        than the target sum.
        """
        l = 0
        r = len(numbers) - 1

        while l < r: # TODO: Double-check this condition.
            current_sum = numbers[l] + numbers[r]
            if current_sum == target:
                return [l+1, r+1]
            elif current_sum < target:
                l += 1
            else:
                r -= 1