167. Two Sum II - Input Array Is Sorted

Given a 1-indexed 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 1 <= index1 < index2 <= numbers.length

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].

Constraints:

• 2 <= numbers.length <= 3 * 10^4
• -1000 <= numbers[i] <= 1000
• numbers is sorted in non-decreasing order.
• -1000 <= target <= 1000
• The tests are generated such that there is exactly one solution.

Approach

Solution

class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        i = 0
        j = len(numbers) - 1

        while i < j:
            c = numbers[i] + numbers[j]
            if c == target:
                return [i + 1, j + 1]
            elif c < target:
                i+=1
            else:
                j-=1
        return []

Explanation