每日算法题: Multitasking

Hi, here's your problem today. This problem was recently asked by AirBNB:

We have a list of tasks to perform, with a cooldown period. We can do multiple of these at the same time, but we cannot run the same task simultaneously.

Given a list of tasks, find how long it will take to complete the tasks in the order they are input.
tasks = [1, 1, 2, 1]
cooldown = 2
output: 7 (order is 1 _ _ 1 2 _ 1)
def findTime(arr, cooldown):
# Fill this in.

print findTime([1, 1, 2, 1], 2)
# 7