mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-12-05 02:40:16 +00:00
a7cd633bb6
* Fix astar
Single character variable names are old school.
* fixup! Format Python code with psf/black push
* Tuple
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
66 lines
1.9 KiB
Python
66 lines
1.9 KiB
Python
"""
|
|
Kadane's algorithm to get maximum subarray sum
|
|
https://medium.com/@rsinghal757/kadanes-algorithm-dynamic-programming-how-and-why-does-it-work-3fd8849ed73d
|
|
https://en.wikipedia.org/wiki/Maximum_subarray_problem
|
|
"""
|
|
test_data: tuple = ([-2, -8, -9], [2, 8, 9], [-1, 0, 1], [0, 0], [])
|
|
|
|
|
|
def negative_exist(arr: list) -> int:
|
|
"""
|
|
>>> negative_exist([-2,-8,-9])
|
|
-2
|
|
>>> [negative_exist(arr) for arr in test_data]
|
|
[-2, 0, 0, 0, 0]
|
|
"""
|
|
arr = arr or [0]
|
|
max = arr[0]
|
|
for i in arr:
|
|
if i >= 0:
|
|
return 0
|
|
elif max <= i:
|
|
max = i
|
|
return max
|
|
|
|
|
|
def kadanes(arr: list) -> int:
|
|
"""
|
|
If negative_exist() returns 0 than this function will execute
|
|
else it will return the value return by negative_exist function
|
|
|
|
For example: arr = [2, 3, -9, 8, -2]
|
|
Initially we set value of max_sum to 0 and max_till_element to 0 than when
|
|
max_sum is less than max_till particular element it will assign that value to
|
|
max_sum and when value of max_till_sum is less than 0 it will assign 0 to i
|
|
and after that whole process, return the max_sum
|
|
So the output for above arr is 8
|
|
|
|
>>> kadanes([2, 3, -9, 8, -2])
|
|
8
|
|
>>> [kadanes(arr) for arr in test_data]
|
|
[-2, 19, 1, 0, 0]
|
|
"""
|
|
max_sum = negative_exist(arr)
|
|
if max_sum < 0:
|
|
return max_sum
|
|
|
|
max_sum = 0
|
|
max_till_element = 0
|
|
|
|
for i in arr:
|
|
max_till_element += i
|
|
if max_sum <= max_till_element:
|
|
max_sum = max_till_element
|
|
if max_till_element < 0:
|
|
max_till_element = 0
|
|
return max_sum
|
|
|
|
|
|
if __name__ == "__main__":
|
|
try:
|
|
print("Enter integer values sepatated by spaces")
|
|
arr = [int(x) for x in input().split()]
|
|
print(f"Maximum subarray sum of {arr} is {kadanes(arr)}")
|
|
except ValueError:
|
|
print("Please enter integer values.")
|