First value seen twice in a left-to-right scan
Walk an integer array from left to right and return the first value you meet for the second time, or -1 when no value repeats. The answer is decided by where the second occurrence happens, not by the smallest repeated value. Give the hash-set solution and discuss what you would do with no extra memory.
MicrosoftCodingNo answer yet. Write the first one; the best answer gets endorsed.