Array Element Parity

ArrayHash Table

Given an array of integers where each integer except one appears exactly twice (once positive, once negative), find the integer that has no corresponding negative/positive counterpart. This integer could be zero, for which the rule still applies: it should appear twice if valid. Your task is to find and return this single integer.

Example 1

Input

[
  1,
  -1,
  2,
  -2,
  3
]

Output

Explanation. All numbers except 3 have their negative counterparts.

Example 2

Input

[
  -4,
  4,
  7,
  -7,
  6,
  -6,
  0
]

Output

Explanation. All numbers have their counterparts, even zero appears as required.

Example 3

Input

[
  -1,
  1,
  -2,
  2,
  0,
  0,
  5
]

Output

Explanation. 5 is the only number without a negative counterpart.

Follow-up: What would be the space complexity if the problem constraint was relaxed to integers appearing 'n' times, still requiring to find one that appears 'n - 1' times?

Constraints:

1. The array will contain at least one element.\n2. Every integer in the array, except one, will appear exactly twice: once as a positive number and once as its negative counterpart.

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