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#325 Finding the Number Without a Pair in an Array

Companies:
Sberbank Diasoft
Themes:
AlgorithmsArraysPractice

An array contains numbers where every number except one has a pair, meaning it occurs twice. Find the number that occurs only once: 

// <= [1, 0, 3, -2, 9, 9, 1, -2, 0]
// => 3

int find(int[] arr) {
    ...
}

Additional conditions:

  • null or an empty array -> throw RuntimeException.
  • More than one number without a pair -> throw RuntimeException.
  • No number occurs exactly once -> throw RuntimeException.
  • Any number occurs more than twice -> throw RuntimeException.

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