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Consolidate duplicate implementations of max subarray (#8849)

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* 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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8
DIRECTORY.md
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@ -293,7 +293,7 @@
* [Inversions](divide_and_conquer/inversions.py)
* [Kth Order Statistic](divide_and_conquer/kth_order_statistic.py)
* [Max Difference Pair](divide_and_conquer/max_difference_pair.py)
* [Max Subarray Sum](divide_and_conquer/max_subarray_sum.py)
* [Max Subarray](divide_and_conquer/max_subarray.py)
* [Mergesort](divide_and_conquer/mergesort.py)
* [Peak](divide_and_conquer/peak.py)
* [Power](divide_and_conquer/power.py)
@ -324,8 +324,7 @@
* [Matrix Chain Order](dynamic_programming/matrix_chain_order.py)
* [Max Non Adjacent Sum](dynamic_programming/max_non_adjacent_sum.py)
* [Max Product Subarray](dynamic_programming/max_product_subarray.py)
* [Max Sub Array](dynamic_programming/max_sub_array.py)
* [Max Sum Contiguous Subsequence](dynamic_programming/max_sum_contiguous_subsequence.py)
* [Max Subarray Sum](dynamic_programming/max_subarray_sum.py)
* [Min Distance Up Bottom](dynamic_programming/min_distance_up_bottom.py)
* [Minimum Coin Change](dynamic_programming/minimum_coin_change.py)
* [Minimum Cost Path](dynamic_programming/minimum_cost_path.py)
@ -591,12 +590,10 @@
* [Is Square Free](maths/is_square_free.py)
* [Jaccard Similarity](maths/jaccard_similarity.py)
* [Juggler Sequence](maths/juggler_sequence.py)
* [Kadanes](maths/kadanes.py)
* [Karatsuba](maths/karatsuba.py)
* [Krishnamurthy Number](maths/krishnamurthy_number.py)
* [Kth Lexicographic Permutation](maths/kth_lexicographic_permutation.py)
* [Largest Of Very Large Numbers](maths/largest_of_very_large_numbers.py)
* [Largest Subarray Sum](maths/largest_subarray_sum.py)
* [Least Common Multiple](maths/least_common_multiple.py)
* [Line Length](maths/line_length.py)
* [Liouville Lambda](maths/liouville_lambda.py)
@ -733,7 +730,6 @@
* [Linear Congruential Generator](other/linear_congruential_generator.py)
* [Lru Cache](other/lru_cache.py)
* [Magicdiamondpattern](other/magicdiamondpattern.py)
* [Maximum Subarray](other/maximum_subarray.py)
* [Maximum Subsequence](other/maximum_subsequence.py)
* [Nested Brackets](other/nested_brackets.py)
* [Number Container System](other/number_container_system.py)

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divide_and_conquer/max_subarray.py Normal file
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"""
The maximum subarray problem is the task of finding the continuous subarray that has the
maximum sum within a given array of numbers. For example, given the array
[-2, 1, -3, 4, -1, 2, 1, -5, 4], the contiguous subarray with the maximum sum is
[4, -1, 2, 1], which has a sum of 6.
This divide-and-conquer algorithm finds the maximum subarray in O(n log n) time.
"""
from __future__ import annotations
import time
from collections.abc import Sequence
from random import randint
from matplotlib import pyplot as plt
def max_subarray(
arr: Sequence[float], low: int, high: int
) -> tuple[int | None, int | None, float]:
"""
Solves the maximum subarray problem using divide and conquer.
:param arr: the given array of numbers
:param low: the start index
:param high: the end index
:return: the start index of the maximum subarray, the end index of the
maximum subarray, and the maximum subarray sum
>>> nums = [-2, 1, -3, 4, -1, 2, 1, -5, 4]
>>> max_subarray(nums, 0, len(nums) - 1)
(3, 6, 6)
>>> nums = [2, 8, 9]
>>> max_subarray(nums, 0, len(nums) - 1)
(0, 2, 19)
>>> nums = [0, 0]
>>> max_subarray(nums, 0, len(nums) - 1)
(0, 0, 0)
>>> nums = [-1.0, 0.0, 1.0]
>>> max_subarray(nums, 0, len(nums) - 1)
(2, 2, 1.0)
>>> nums = [-2, -3, -1, -4, -6]
>>> max_subarray(nums, 0, len(nums) - 1)
(2, 2, -1)
>>> max_subarray([], 0, 0)
(None, None, 0)
"""
if not arr:
return None, None, 0
if low == high:
return low, high, arr[low]
mid = (low + high) // 2
left_low, left_high, left_sum = max_subarray(arr, low, mid)
right_low, right_high, right_sum = max_subarray(arr, mid + 1, high)
cross_left, cross_right, cross_sum = max_cross_sum(arr, low, mid, high)
if left_sum >= right_sum and left_sum >= cross_sum:
return left_low, left_high, left_sum
elif right_sum >= left_sum and right_sum >= cross_sum:
return right_low, right_high, right_sum
return cross_left, cross_right, cross_sum
def max_cross_sum(
arr: Sequence[float], low: int, mid: int, high: int
) -> tuple[int, int, float]:
left_sum, max_left = float("-inf"), -1
right_sum, max_right = float("-inf"), -1
summ: int | float = 0
for i in range(mid, low - 1, -1):
summ += arr[i]
if summ > left_sum:
left_sum = summ
max_left = i
summ = 0
for i in range(mid + 1, high + 1):
summ += arr[i]
if summ > right_sum:
right_sum = summ
max_right = i
return max_left, max_right, (left_sum + right_sum)
def time_max_subarray(input_size: int) -> float:
arr = [randint(1, input_size) for _ in range(input_size)]
start = time.time()
max_subarray(arr, 0, input_size - 1)
end = time.time()
return end - start
def plot_runtimes() -> None:
input_sizes = [10, 100, 1000, 10000, 50000, 100000, 200000, 300000, 400000, 500000]
runtimes = [time_max_subarray(input_size) for input_size in input_sizes]
print("No of Inputs\t\tTime Taken")
for input_size, runtime in zip(input_sizes, runtimes):
print(input_size, "\t\t", runtime)
plt.plot(input_sizes, runtimes)
plt.xlabel("Number of Inputs")
plt.ylabel("Time taken in seconds")
plt.show()
if __name__ == "__main__":
"""
A random simulation of this algorithm.
"""
from doctest import testmod
testmod()

78
divide_and_conquer/max_subarray_sum.py
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"""
Given a array of length n, max_subarray_sum() finds
the maximum of sum of contiguous sub-array using divide and conquer method.
Time complexity : O(n log n)
Ref : INTRODUCTION TO ALGORITHMS THIRD EDITION
(section : 4, sub-section : 4.1, page : 70)
"""
def max_sum_from_start(array):
"""This function finds the maximum contiguous sum of array from 0 index
Parameters :
array (list[int]) : given array
Returns :
max_sum (int) : maximum contiguous sum of array from 0 index
"""
array_sum = 0
max_sum = float("-inf")
for num in array:
array_sum += num
if array_sum > max_sum:
max_sum = array_sum
return max_sum
def max_cross_array_sum(array, left, mid, right):
"""This function finds the maximum contiguous sum of left and right arrays
Parameters :
array, left, mid, right (list[int], int, int, int)
Returns :
(int) : maximum of sum of contiguous sum of left and right arrays
"""
max_sum_of_left = max_sum_from_start(array[left : mid + 1][::-1])
max_sum_of_right = max_sum_from_start(array[mid + 1 : right + 1])
return max_sum_of_left + max_sum_of_right
def max_subarray_sum(array, left, right):
"""Maximum contiguous sub-array sum, using divide and conquer method
Parameters :
array, left, right (list[int], int, int) :
given array, current left index and current right index
Returns :
int : maximum of sum of contiguous sub-array
"""
# base case: array has only one element
if left == right:
return array[right]
# Recursion
mid = (left + right) // 2
left_half_sum = max_subarray_sum(array, left, mid)
right_half_sum = max_subarray_sum(array, mid + 1, right)
cross_sum = max_cross_array_sum(array, left, mid, right)
return max(left_half_sum, right_half_sum, cross_sum)
if __name__ == "__main__":
array = [-2, -5, 6, -2, -3, 1, 5, -6]
array_length = len(array)
print(
"Maximum sum of contiguous subarray:",
max_subarray_sum(array, 0, array_length - 1),
)

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dynamic_programming/max_sub_array.py
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"""
author : Mayank Kumar Jha (mk9440)
"""
from __future__ import annotations
def find_max_sub_array(a, low, high):
if low == high:
return low, high, a[low]
else:
mid = (low + high) // 2
left_low, left_high, left_sum = find_max_sub_array(a, low, mid)
right_low, right_high, right_sum = find_max_sub_array(a, mid + 1, high)
cross_left, cross_right, cross_sum = find_max_cross_sum(a, low, mid, high)
if left_sum >= right_sum and left_sum >= cross_sum:
return left_low, left_high, left_sum
elif right_sum >= left_sum and right_sum >= cross_sum:
return right_low, right_high, right_sum
else:
return cross_left, cross_right, cross_sum
def find_max_cross_sum(a, low, mid, high):
left_sum, max_left = -999999999, -1
right_sum, max_right = -999999999, -1
summ = 0
for i in range(mid, low - 1, -1):
summ += a[i]
if summ > left_sum:
left_sum = summ
max_left = i
summ = 0
for i in range(mid + 1, high + 1):
summ += a[i]
if summ > right_sum:
right_sum = summ
max_right = i
return max_left, max_right, (left_sum + right_sum)
def max_sub_array(nums: list[int]) -> int:
"""
Finds the contiguous subarray which has the largest sum and return its sum.
>>> max_sub_array([-2, 1, -3, 4, -1, 2, 1, -5, 4])
6
An empty (sub)array has sum 0.
>>> max_sub_array([])
0
If all elements are negative, the largest subarray would be the empty array,
having the sum 0.
>>> max_sub_array([-1, -2, -3])
0
>>> max_sub_array([5, -2, -3])
5
>>> max_sub_array([31, -41, 59, 26, -53, 58, 97, -93, -23, 84])
187
"""
best = 0
current = 0
for i in nums:
current += i
current = max(current, 0)
best = max(best, current)
return best
if __name__ == "__main__":
"""
A random simulation of this algorithm.
"""
import time
from random import randint
from matplotlib import pyplot as plt
inputs = [10, 100, 1000, 10000, 50000, 100000, 200000, 300000, 400000, 500000]
tim = []
for i in inputs:
li = [randint(1, i) for j in range(i)]
strt = time.time()
(find_max_sub_array(li, 0, len(li) - 1))
end = time.time()
tim.append(end - strt)
print("No of Inputs Time Taken")
for i in range(len(inputs)):
print(inputs[i], "\t\t", tim[i])
plt.plot(inputs, tim)
plt.xlabel("Number of Inputs")
plt.ylabel("Time taken in seconds ")
plt.show()

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dynamic_programming/max_subarray_sum.py Normal file
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"""
The maximum subarray sum problem is the task of finding the maximum sum that can be
obtained from a contiguous subarray within a given array of numbers. For example, given
the array [-2, 1, -3, 4, -1, 2, 1, -5, 4], the contiguous subarray with the maximum sum
is [4, -1, 2, 1], so the maximum subarray sum is 6.
Kadane's algorithm is a simple dynamic programming algorithm that solves the maximum
subarray sum problem in O(n) time and O(1) space.
Reference: https://en.wikipedia.org/wiki/Maximum_subarray_problem
"""
from collections.abc import Sequence
def max_subarray_sum(
arr: Sequence[float], allow_empty_subarrays: bool = False
) -> float:
"""
Solves the maximum subarray sum problem using Kadane's algorithm.
:param arr: the given array of numbers
:param allow_empty_subarrays: if True, then the algorithm considers empty subarrays
>>> max_subarray_sum([2, 8, 9])
19
>>> max_subarray_sum([0, 0])
0
>>> max_subarray_sum([-1.0, 0.0, 1.0])
1.0
>>> max_subarray_sum([1, 2, 3, 4, -2])
10
>>> max_subarray_sum([-2, 1, -3, 4, -1, 2, 1, -5, 4])
6
>>> max_subarray_sum([2, 3, -9, 8, -2])
8
>>> max_subarray_sum([-2, -3, -1, -4, -6])
-1
>>> max_subarray_sum([-2, -3, -1, -4, -6], allow_empty_subarrays=True)
0
>>> max_subarray_sum([])
0
"""
if not arr:
return 0
max_sum = 0 if allow_empty_subarrays else float("-inf")
curr_sum = 0.0
for num in arr:
curr_sum = max(0 if allow_empty_subarrays else num, curr_sum + num)
max_sum = max(max_sum, curr_sum)
return max_sum
if __name__ == "__main__":
from doctest import testmod
testmod()
nums = [-2, 1, -3, 4, -1, 2, 1, -5, 4]
print(f"{max_subarray_sum(nums) = }")

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dynamic_programming/max_sum_contiguous_subsequence.py
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def max_subarray_sum(nums: list) -> int:
"""
>>> max_subarray_sum([6 , 9, -1, 3, -7, -5, 10])
17
"""
if not nums:
return 0
n = len(nums)
res, s, s_pre = nums[0], nums[0], nums[0]
for i in range(1, n):
s = max(nums[i], s_pre + nums[i])
s_pre = s
res = max(res, s)
return res
if __name__ == "__main__":
nums = [6, 9, -1, 3, -7, -5, 10]
print(max_subarray_sum(nums))

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maths/kadanes.py
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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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maths/largest_subarray_sum.py
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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))))

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other/maximum_subarray.py
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from collections.abc import Sequence
def max_subarray_sum(nums: Sequence[int]) -> int:
"""Return the maximum possible sum amongst all non - empty subarrays.
Raises:
ValueError: when nums is empty.
>>> max_subarray_sum([1,2,3,4,-2])
10
>>> max_subarray_sum([-2,1,-3,4,-1,2,1,-5,4])
6
"""
if not nums:
raise ValueError("Input sequence should not be empty")
curr_max = ans = nums[0]
nums_len = len(nums)
for i in range(1, nums_len):
num = nums[i]
curr_max = max(curr_max + num, num)
ans = max(curr_max, ans)
return ans
if __name__ == "__main__":
n = int(input("Enter number of elements : ").strip())
array = list(map(int, input("\nEnter the numbers : ").strip().split()))[:n]
print(max_subarray_sum(array))