mirror of
https://github.com/TheAlgorithms/Python.git
synced 2025-03-28 09:26:44 +00:00
580273eeca
* Update prefix_sum.py Index Validation for get_sum Raises ValueError if start or end is out of range or start > end. Handles cases where the array is empty. ✅ Empty Array Support If an empty array is passed, get_sum raises an appropriate error instead of failing unexpectedly. ✅ Optimized contains_sum Initialization Initializes sums with {0} for efficient subarray sum checking. * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Update prefix_sum.py * Update prefix_sum.py * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Update prefix_sum.py * Update prefix_sum.py --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>
97 lines
2.5 KiB
Python
97 lines
2.5 KiB
Python
"""
|
|
Author : Alexander Pantyukhin
|
|
Date : November 3, 2022
|
|
|
|
Implement the class of prefix sum with useful functions based on it.
|
|
|
|
"""
|
|
|
|
|
|
class PrefixSum:
|
|
def __init__(self, array: list[int]) -> None:
|
|
len_array = len(array)
|
|
self.prefix_sum = [0] * len_array
|
|
|
|
if len_array > 0:
|
|
self.prefix_sum[0] = array[0]
|
|
|
|
for i in range(1, len_array):
|
|
self.prefix_sum[i] = self.prefix_sum[i - 1] + array[i]
|
|
|
|
def get_sum(self, start: int, end: int) -> int:
|
|
"""
|
|
The function returns the sum of array from the start to the end indexes.
|
|
Runtime : O(1)
|
|
Space: O(1)
|
|
|
|
>>> PrefixSum([1,2,3]).get_sum(0, 2)
|
|
6
|
|
>>> PrefixSum([1,2,3]).get_sum(1, 2)
|
|
5
|
|
>>> PrefixSum([1,2,3]).get_sum(2, 2)
|
|
3
|
|
>>> PrefixSum([]).get_sum(0, 0)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: The array is empty.
|
|
>>> PrefixSum([1,2,3]).get_sum(-1, 2)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: Invalid range specified.
|
|
>>> PrefixSum([1,2,3]).get_sum(2, 3)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: Invalid range specified.
|
|
>>> PrefixSum([1,2,3]).get_sum(2, 1)
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: Invalid range specified.
|
|
"""
|
|
if not self.prefix_sum:
|
|
raise ValueError("The array is empty.")
|
|
|
|
if start < 0 or end >= len(self.prefix_sum) or start > end:
|
|
raise ValueError("Invalid range specified.")
|
|
|
|
if start == 0:
|
|
return self.prefix_sum[end]
|
|
|
|
return self.prefix_sum[end] - self.prefix_sum[start - 1]
|
|
|
|
def contains_sum(self, target_sum: int) -> bool:
|
|
"""
|
|
The function returns True if array contains the target_sum,
|
|
False otherwise.
|
|
|
|
Runtime : O(n)
|
|
Space: O(n)
|
|
|
|
>>> PrefixSum([1,2,3]).contains_sum(6)
|
|
True
|
|
>>> PrefixSum([1,2,3]).contains_sum(5)
|
|
True
|
|
>>> PrefixSum([1,2,3]).contains_sum(3)
|
|
True
|
|
>>> PrefixSum([1,2,3]).contains_sum(4)
|
|
False
|
|
>>> PrefixSum([1,2,3]).contains_sum(7)
|
|
False
|
|
>>> PrefixSum([1,-2,3]).contains_sum(2)
|
|
True
|
|
"""
|
|
|
|
sums = {0}
|
|
for sum_item in self.prefix_sum:
|
|
if sum_item - target_sum in sums:
|
|
return True
|
|
|
|
sums.add(sum_item)
|
|
|
|
return False
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|