Two Sum and Array Algorithms | Dataford Interview Questions

Fundbox needs to identify two payment amounts whose combined value matches a requested total. Given an unsorted array, return the lexicographically smallest pair of distinct indices [i, j] where i < j and nums[i] + nums[j] == target.

If multiple pairs match, choose the pair with the smallest i. If several pairs have the same i, choose the smallest j. Return [] when no valid pair exists.

You may not use the same array element twice.

Formal Specification

Implement find_payment_pair(nums, target):

Input: nums, a list of integers, and target, an integer.
Output: a two-element list containing the selected indices, or an empty list if no pair exists.
Indices are zero-based.

Constraints

0 <= nums.length <= 100,000
-10^9 <= nums[i] <= 10^9
-10^9 <= target <= 10^9
The input may contain duplicate values
There may be zero, one, or multiple valid pairs

Function Signature

def find_payment_pair(nums, target):

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