167. Two Sum II - Input array is sorted

🟩 Easy

Question

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2.

Note:

• Your returned answers (both index1 and index2) are not zero-based.

• You may assume that each input would have exactly one solution and you may not use the same element twice.

Example:

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.

Code

def twoSum(self, numbers: List[int], target: int) -> List[int]:
    l, r = 0, len(numbers) - 1
    while (l < r):
        if numbers[l] + numbers[r] == target:
            return [l+1, r+1]
        elif numbers[l] + numbers[r] > target: 
            r -= 1
        else:
            l += 1