Added counting sort for Python

Author: b72u68

Python/Algorithms/Sorting/counting_sort.py

@@ -0,0 +1,57 @@
+def counting_sort(A, max_val):
+ """
+ This soring algorithm will only works with array length n consist of
+ elements from 0 to k for integer k < n.
+ """
+ k = max_val + 1
+ count = [0]*k
+ result = [None]*len(A)
+
+ print("Array A = ", A)
+
+ # counting the number of i (1 < i < k) in A and store in count
+ for i in A:
+ count[i] += 1
+
+ print("Counting array (storing number of elements appear in A) = ", count)
+
+ # calculate the position of each element in the sorted array
+ for i in range(1, len(count)):
+ count[i] = count[i] + count[i-1]
+
+ print("Counting array (storing order of elements appear in A) = ", count)
+
+ # store the elements back in result using the position of elements stored in count
+ for i in range(len(A)-1, -1, -1):
+ result[count[A[i]]-1] = A[i]
+ count[A[i]] -= 1
+
+ return result
+
+import random
+
+# test function
+def test():
+ while True:
+ try:
+ n = int(input("Enter length of array A (n): "))
+ max_val = int(input("Enter the max val in A (smaller than n): "))
+
+ if max_val >= n:
+ print("Invalid input.\n")
+
+ else:
+ A = []
+
+ for _ in range(n):
+ A.append(random.randint(0, max_val))
+
+ print("\nResult: ", counting_sort(A, max_val), "\n")
+
+ except Exception as e:
+ print(e)
+ print("Exiting...\n")
+ break
+
+if __name__ == "__main__":
+ test()