Two sum II - Input array is sorted

Two sum II：

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：

class Solution:
    def twoSum(self, numbers, target):
        """
        :type numbers: List[int]
        :type target: int
        :rtype: List[int]
        """
        index_1=0
        index_2=len(numbers)-1
        while index_1<index_2:
            if numbers[index_1]+numbers[index_2] == target:
                return [index_1+1,index_2+1]
            if numbers[index_1]+numbers[index_2] > target:
                index_2=index_2-1
            else:
                index_1=index_1+1