Teaching Kids Programming: Videos on Data Structures and Algorithms
The accumulate function is provided in itertools and allows us to return a generator containing the sum of previous items. For example:
1 2 3 4 5 6 | from itertools import accumulate a = [1, 2, 3, 4, 5] print(accumulate(a)) <itertools.accumulate object at 0xa770d0> list(accumulate(a)) [1, 3, 6, 10, 15] |
from itertools import accumulate a = [1, 2, 3, 4, 5] print(accumulate(a)) <itertools.accumulate object at 0xa770d0> list(accumulate(a)) [1, 3, 6, 10, 15]
We can define an accumulate function that returns a list:
1 2 3 4 | def accumulate(a): for i in range(1, len(a)): a[i] += a[i - 1] return a |
def accumulate(a):
for i in range(1, len(a)):
a[i] += a[i - 1]
return aWe can also make it return a generator:
1 2 3 4 | def accumulate(a): for i in range(1, len(a)): a[i] += a[i - 1] yield from a |
def accumulate(a):
for i in range(1, len(a)):
a[i] += a[i - 1]
yield from aIf we want to not modify the original list:
1 2 3 4 5 | def accumulate(a): b = [a[0]] for i in range(1, len(a)): b.append(a[i] + b[-1]) yield from b |
def accumulate(a):
b = [a[0]]
for i in range(1, len(a)):
b.append(a[i] + b[-1])
yield from bTime complexity is O(N) where N is the number of elements in the list.
See also: Teaching Kids Programming – Matrix Prefix Sum Algorithm
–EOF (The Ultimate Computing & Technology Blog) —
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