':type target: int
:rtype: int'

def pick(self, target):

    reservoir = (-1)
    n = 0
    for i in xrange(len(self.__nums)):
        if (self.__nums[i] != target):
            continue
        reservoir = (i if ((n == 0) or (randint(1, (n + 1)) == 1)) else reservoir)
        n += 1
    return reservoir
