#Given an array replace every element by product of previous and next
#first element is replaced by product of first and second and last element by product of last and second last
#Time-complexity: O(n),Auxiliary-space: O(1)



def modify(a)
    len=a.length
    if len<=0
        return -1
    end
    #update first element
    prev=a[0]
    a[0]*=a[1]
    for i in 1...len-1
        current=a[i]        #Keep track of current element
        a[i]=prev*a[i+1]
        prev=current        #Store current element for next iteration
    end
     #update last element
    a[len-1]*=prev
    return a
end
modify([3,6,1,7,8,2]) # => [18, 3, 42, 8, 14, 16]