Consolidate duplicate implementations of max subarray (#8849)

* Remove max subarray sum duplicate implementations

* updating DIRECTORY.md

* Rename max_sum_contiguous_subsequence.py

* Fix typo in dynamic_programming/max_subarray_sum.py

* Remove duplicate divide and conquer max subarray

* updating DIRECTORY.md

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Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
This commit is contained in:
Tianyi Zheng
2023-07-11 02:44:12 -07:00
committed by GitHub
parent c9ee6ed188
commit a0eec90466
9 changed files with 174 additions and 313 deletions

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"""
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_number = arr[0]
for i in arr:
if i >= 0:
return 0
elif max_number <= i:
max_number = i
return max_number
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
max_sum = max(max_sum, max_till_element)
max_till_element = max(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.")

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from sys import maxsize
def max_sub_array_sum(a: list, size: int = 0):
"""
>>> max_sub_array_sum([-13, -3, -25, -20, -3, -16, -23, -12, -5, -22, -15, -4, -7])
-3
"""
size = size or len(a)
max_so_far = -maxsize - 1
max_ending_here = 0
for i in range(0, size):
max_ending_here = max_ending_here + a[i]
max_so_far = max(max_so_far, max_ending_here)
max_ending_here = max(max_ending_here, 0)
return max_so_far
if __name__ == "__main__":
a = [-13, -3, -25, -20, 1, -16, -23, -12, -5, -22, -15, -4, -7]
print(("Maximum contiguous sum is", max_sub_array_sum(a, len(a))))