Two Sum II Input Array Is Sorted

Medium · Two Pointers

You are given a list of integers that is already sorted in non-decreasing order, along with a target value. Find the two distinct positions (1-indexed) whose values add up exactly to the target, and return them as a two-element list with the smaller index first. You may assume exactly one valid pair exists, and you cannot use the same element twice.

Examples

Input:  numbers = [2,7,11,15], target = 9
Output: [1,2]
Why:    numbers[0] + numbers[1] = 2 + 7 = 9, so the 1-indexed positions are 1 and 2.

Input:  numbers = [2,3,4], target = 6
Output: [1,3]
Why:    numbers[0] + numbers[2] = 2 + 4 = 6, giving positions 1 and 3.

Input:  numbers = [-1,0], target = -1
Output: [1,2]
Why:    numbers[0] + numbers[1] = -1 + 0 = -1, giving positions 1 and 2.

Constraints

2 <= numbers.length <= 3*10^4, -1000 <= numbers[i] <= 1000, numbers is sorted in non-decreasing order, -1000 <= target <= 1000, exactly one valid answer exists

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This statement is written for CodeSpeek. The problem is part of the NeetCode 150 list; Watch NeetCode's explanation of Two Sum II Input Array Is Sorted. Reference solutions from the NeetCode repository (MIT) are used to verify our tests.