Two Sum II - Input array is sorted

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.

Solution 1

• Time complexity: O(n)
• Space complexity: O(n)

class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        # O(n) time complexity
        # O(n) space complexity  
        bag = {}
        
        for i, num in enumerate(numbers):            
            if num in bag:
                return [bag[num], i+1]
            bag[target - num] = i + 1

Solution 2:

• Using Two pointers
  • Time complexity: O(n)
  • Space complexity: O(1)

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