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Kadane's algorithm for maximum sum contiguous subarray#39

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1 change: 1 addition & 0 deletionsallalgorithms/subarray/__init__.py
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from .kadane import *
44 changes: 44 additions & 0 deletionsallalgorithms/subarray/kadane.py
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# -*- coding: UTF-8 -*-
#
# Kadane's Algorithm
# The All ▲lgorithms library for python
#
# Contributed by: Kunal Keshav Singh Sahni
# Github: @kunal768
#

import sys

def maxsum_subarray(arr):
curr = arr[0]
maxx = arr[0]
n = len(arr)

for i in range(1,n):
curr = max(arr[i],curr+arr[i])
maxx = max(curr,maxx)

return maxx


def returnArray(arr):
size = len(arr)
max_so_far = -sys.maxsize - 1
max_ending_here = 0
start = 0
end = 0
s = 0
for i in range(0,size):

max_ending_here += arr[i]

if max_so_far < max_ending_here:
max_so_far = max_ending_here
start = s
end = i

if max_ending_here < 0:
max_ending_here = 0
s = i+1

return [max_so_far,arr[start:end+1]]
7 changes: 6 additions & 1 deletiondocs/readme.md
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Expand Up@@ -69,10 +69,15 @@ print(binary_search(arr, 3))
- [Merge Sort](https://python.allalgorithms.com/sorting/merge-sort)
- [Pigeonhole Sort](https://python.allalgorithms.com/sorting/pigeonhole-sort)
- [Selection Sort](https://python.allalgorithms.com/sorting/selection-sort)
- [Stooge Sort](https://python.allalgorithms.com/sorting/stooge-sort)
- [Stooge Sort](https://python.allalgorithms.com/sorting/stooge-sor

- ### String
- [Palindrome Check](https://python.allalgorithms.com/string/palindrom-check)

- ### Subarray
- [Kadane's Algorithm](https://github.com/kunal768/allalgorithms-python/blob/master/allalgorithms/subarray/kadane.py)


# Related

- [allalgorithms-javascript](https://github.com/abranhe/allalgorithms-javascript): All ▲lgorithms Javascript library
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36 changes: 36 additions & 0 deletionsdocs/subarray/kadane.md
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# Kadane's Algorithm

Kadane’s algorithm is to look for all positive contiguous segments of the array (max_ending_here is used for this). And keep track of maximum sum contiguous segment among all positive segments (max_so_far is used for this) Each time we get a positive sum compare it with max_so_far and update max_so_far if it is greater than max_so_far
## Install

```
pip install allalgorithms
```

## Usage

```py
from allalgorithms.subarray import kadane

arr = [-2, 1, 2, 7, 10, 77]

print(kadane.maxsum_subarray(arr))
# -> 97

print(kadane.returnArray(arr))
# -> [97, [1, 2, 7, 10, 77]]
```

## API

### maxsum_subarray(array)

> Return sum of maximum contigious subarray

### returnArray(array)

> Return sum along with the respective subarray

##### Params:

- `array`: Array (may contain negative elements)
5 changes: 5 additions & 0 deletionsreadme.md
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Expand Up@@ -70,9 +70,14 @@ print(binary_search(arr, 3))
- [Pigeonhole Sort](https://python.allalgorithms.com/sorting/pigeonhole-sort)
- [Selection Sort](https://python.allalgorithms.com/sorting/selection-sort)
- [Stooge Sort](https://python.allalgorithms.com/sorting/stooge-sort)

- ### String
- [Palindrome Check](https://python.allalgorithms.com/string/palindrom-check)

- ### Subarray
- [Kadane's Algorithm](https://python.allalgorithms.com/subarray/kadane)


# Related

- [allalgorithms-javascript](https://github.com/abranhe/allalgorithms-javascript): All ▲lgorithms Javascript library
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19 changes: 19 additions & 0 deletionstests/test_kadane.py
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import unittest

from allalgorithms.subarray import kadane

class TestSearches(unittest.TestCase):
def test_returnArray(self):
self.assertEqual( [11,[2,3,-1,7]], kadane.returnArray([2,3,-1,7]))
self.assertEqual([5,[2,3]], kadane.returnArray([2,3,-2,4]))
self.assertEqual([0, [0]], kadane.returnArray([-1,-1,-0,0]))
self.assertEqual([-1, [-1]], kadane.returnArray([-1]))

def test_maxsum_subarray(self):
self.assertEqual(11,kadane.maxsum_subarray([2,3,-1,7]))
self.assertEqual(5, kadane.maxsum_subarray([2,3,-2,4]))
self.assertEqual(0, kadane.maxsum_subarray([-1,-1,-0,0]))
self.assertEqual(-1, kadane.maxsum_subarray([-1]))

if __name__ == '__main__':
unittest.main()
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