Medium

Quiz

#167 Two Sum II - Input Array Is Sorted

APPROACH

A 1-indexed integer array numbers is already sorted in non-decreasing order. Find two elements that sum to target: numbers[index1] and numbers[index2], where 1 <= index1 < index2 <= numbers.length.

Return [index1, index2] (1-based). Exactly one solution exists and no element may be used twice.

Your solution must use only constant extra space.

Example 1:

Input: numbers = [2,7,11,15], target = 9

Output: [1,2]

Explanation: The sum of 2 and 7 is 9. Therefore, index1 = 1, index2 = 2. We return [1, 2].

Example 2:

Input: numbers = [2,3,4], target = 6

Output: [1,3]

Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1, index2 = 3. We return [1, 3].

Example 3:

Input: numbers = [-1,0], target = -1

Output: [1,2]

Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1, index2 = 2. We return [1, 2].

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What is the optimal approach for this problem?