twosumII.py

"Leetcode- https://leetcode.com/problems/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.

Return the indices of the two numbers, index1 and index2, added by one as an integer array [index1, index2] of length 2.

The tests are generated such that there is exactly one solution. You may not use the same element 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].
'''
def twoSum(self, numbers, target):
    l, r = 0, len(numbers)-1
    while l < r:
        sum = numbers[l] + numbers[r]
        if sum < target:
            l += 1
        elif sum > target:
            r -= 1
        else:
            return [l+1, r+1]

#T:O(N)
#S:O(1)