擅长:python、mysql、java
<pre><code>def double_preceding(values):
"""(list) -> NoneType
Replace each item in the list with twice the value of the preceding item, and replace the first item with 0.
>>> L = [1 , 2 , 3]
>>> double_preceding(L)
>>> L
(0, 2, 4]
"""
if values != []:
temp = values[0] # temp is 1 now
values[0] = 0 #sets 1 to 0
for i in range(1, len(values)): # start at second item in array and go until end
double = 2 * temp # double it by the last (which is stored in temp)
temp = values[i] # temp is now equal to the item we just doubled (the "preceding item")
values[i] = double # change the value of the item at the index so it is actually the doubled item
</code></pre>