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Pair Sum Coding Challenge

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Your question is Pair Sum Coding Challenge. Start with the requirements on the right.

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Problem

Photon's frontend event inspector needs to determine whether two event scores in an unsorted array combine to a specified target value. Given an integer array and a target sum, return True if two distinct elements add up to the target, otherwise return False.

The same value may appear multiple times, and each array position can be used at most once. Aim for a single-pass solution that does not modify the input array. After presenting the baseline solution, explain how you would adapt it if the array were already sorted, if memory were limited, or if the input arrived as a stream.

Formal Specification

Implement has_pair_sum(nums, target).

  • Input: nums, a list of integers, and target, an integer.
  • Output: A boolean indicating whether indices i and j exist such that i != j and nums[i] + nums[j] == target.
  • The order of the pair does not matter because only existence is requested.

Constraints

  • 2 <= len(nums) <= 10^6
  • -10^9 <= nums[i] <= 10^9
  • -10^9 <= target <= 10^9
  • Duplicate values are allowed.
  • The input array must not be modified.
  • Expected running time is O(n).

Function Signature

def has_pair_sum(nums, target):
Your solutionPython 3
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