Python3 代码

class Solution(object):
    def duplicateInArray(self, nums):
        """
        :type nums: List[int]
        :rtype int
        """
        for i in nums:
            if i < 0 or i >len(nums)-1:
                return -1
        temp_set = set()
        repeat = -1
        for i in range(len(nums)):
            temp_set.add(nums[i])
            if len(temp_set) < i + 1 :
                repeat = nums[i]
                break
        return repeat