Find two numbers summing to target without hashmap

Q: Find two numbers summing to target without hashmap

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Question

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Problem

Given an integer array nums (length n) and an integer target, return the indices (i, j) such that:

i != j
nums[i] + nums[j] == target

You may assume exactly one valid pair exists.

Constraints

2 <= n <= 2 * 10^5
-10^9 <= nums[k], target <= 10^9

Requirements

Do not use a hash map / hash set solution.
Aim to use sorting + two pointers.
Output must be indices in the original array.

Input/Output

Input: nums , target
Output: a pair of indices [i, j] (order does not matter)

Example

nums = [2, 7, 11, 15] , target = 9 → output could be [0, 1]