class Solution:
    def twoSum(self, numbers, target):
        """
        :type numbers: List[int]
        :type target: int
        :rtype: List[int]
        """
        left, right = 0, len(numbers)-1
        while left < right:
            if numbers[left] + numbers[right] == target:
                return [left+1, right+1]
            elif numbers[left] + numbers[right] < target:
                left += 1
            else:
                right -= 1
        # alternative is to just do binary search but not faster because 
        # you do the search for each number potentially O(n log n)
        