Interview Question: Store Last N order Ids

This problem was asked by Twitter.

You run an e-commerce website and want to record the last N order ids in a log. Implement a data structure to accomplish this, with the following API:

• record(order_id): adds the order_id to the log

• get_last(i): gets the ith last element from the log. i is guaranteed to be smaller than or equal to N.

You should be as efficient with time and space as possible.

Implementation:

class LogData:
 def __init__(self,size):
 self.maxSize = size
 self.circularBuffer = [None] * size
 self.index = 0

 def record(self,orderId):
 self.circularBuffer[self.index] = orderId
 self.index = (self.index + 1) % self.maxSize

 def getLast(self,i):
 return self.circularBuffer[
            (self.index - i + self.maxSize)% self.maxSize]

#Size Of Log
data = LogData(5) 
#Giving Input
data.record(5)
data.record(4)
data.record(6)
data.record(9)
data.record(12)
data.record(90)
data.record(120)
#Get the last third order Id
print(data.getLast(3)) #Output Should be 12

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