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. Please note that 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.
Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

Answer 1

The twoSum function uses a two-pointer approach to find two numbers in a sorted array that add up to a specific target number, returning their indices which are incremented by one to account for the non-zero-based index requirement.

Step-by-step explanation:

The problem you're trying to solve falls under the scope of an algorithmic challenge that is often encountered in Mathematics, especially in the Computer Science field. To find two numbers in a sorted array that add up to a specific target, we can make use of a function twoSum. Since the array is already sorted, a two-pointer approach can be really efficient. Here is a common way to implement this:

1. Place one pointer at the beginning of the array (left) and the other at the end (right).
2. Calculate the sum of the values at the left and right pointer.
3. If the sum is less than the target, move the left pointer up to increase the sum.
4. If the sum is greater than the target, move the right pointer down to decrease the sum.
5. Repeat this process until the sum equals the target.
6. Once the correct numbers are found, return their indices plus one (since the indices are not zero-based).

For the given example with numbers = {2, 7, 11, 15} and target = 9:

• The initial pointers would point to 2 and 15.
• Since 2 + 15 is greater than 9, we move the right pointer down.
• The pointers now point to 2 and 11, but 2 + 11 is still greater than 9, so we move the right pointer down again.
• Finally, the pointers point to 2 and 7, and because 2 + 7 equals 9, we have found our solution.
• The function thus returns index1 = 1 and index2 = 2.