Given an array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 0 <= index1 < index2 < numbers.length.
Return the indices of the two numbers, index1 and index2 as an integer array [index1, index2] of length 2.
You may not use the same element twice.
Your solution must use only constant extra space. i.e. O(1) Space Complexity
Input: numbers = [2,7,11,15], target = 9
Output: [0,1]
Explanation: The sum of 2 and 7 is 9. Therefore, index1 = 0, index2 = 1. We return [0, 1].
Input: numbers = [2,3,4], target = 6
Output: [0,2]
Explanation: The sum of 2 and 4 is 6. Therefore index1 = 0, index2 = 2. We return [0, 2].
Input: numbers = [-1,0], target = -1
Output: [0, 1]
Explanation: The sum of -1 and 0 is -1. Therefore index1 = 0, index2 = 1. We return [0, 1].
This problem was taken from Leetcode: Two Sum II.