Kadanes_algorithm

maths/kadanes_algorithm.py

@@ -0,0 +1,85 @@
+"""
+    Link for the explanation of this algorithm :- 
+    https://medium.com/@rsinghal757/kadanes-algorithm-dynamic-programming-how-and-why-does-it-work-3fd8849ed73d
+    Kadane's algorithm to get maximum subarray sum
+    Please enter the decimal values only and use spaces as separator
+"""
+
+
+"""
+Doc-Test :-
+
+Enter the element of array with spaces  :-
+>>> 2 3 -9 8 -2 
+Maximum subarray sum of  [2, 3, -9, 8, -2] is :- 8
+
+
+Enter the element of array with spaces  :-
+>>> -9 -8 -7 -6 -2
+Maximum subarray sum of  [-9, -8, -7, -6, -2] is :- -2
+
+"""
+def negative_exist(arr):
+
+    """
+     checks whether the max value in -ve or not
+     eg :- 
+      arr = [-2,-8,-9]
+      so max element is negative i.e. -2
+      so answer is -2
+
+      and if max value is positive it will return 0
+      and then apply the kadane's algorithm
+      eg :- 
+      arr = [2,8,-9]
+      positive number exist so it will return 0
+    """
+    max=arr[0]
+    for i in arr:
+        if(i>=0):
+            return 0;
+        elif(max<=i):
+            max=i
+    return max 
+
+
+def kadanes_implementation(arr):
+
+
+    """
+     if negative_exist return 0 than this function will execute
+     else it will return the value return by negative_exist function
+
+     Eg :- 
+     arr = [2,3,-9,8,-2]
+       initially the value of max_sum = 0 and max_till_element is 0
+       than when max_sum 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 whole process it will return the value
+
+       So the output for above arr is :- 8
+    """
+    if negative_exist(arr) < 0:
+        return negative_exist(arr)
+
+    max_sum = 0
+    max_till_element=0
+
+    for i in arr:
+        max_till_element=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 the element of array with spaces  :- ")
+        arr = [int(x) for x in input().split()]
+        print("Maximum subarray sum of ",arr,"is :-",kadanes_implementation(arr))
+    except ValueError:
+        print("Please,enter decimal values")