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| Given an array, there is exactly one value that appears exactly two times. Return that value. findTheDuplicate([1, 7, 1]) → 1 findTheDuplicate([5, 7, 5, 7, 8, 7]) → 5 findTheDuplicate([9, 9]) → 9 ...Save, Compile, Run (ctrl-enter) | 
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Difficulty: 300
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