Changed location of counting_sort.py

(i) Moved the file to sort/ folder
(ii) Added new entry to README.md

Author: ankit167

README.md

@@ -135,6 +135,7 @@ Minimal and clean example implementations of data structures and algorithms in P
     - [sort_colors](sort/sort_colors.py)
     - [topsort](sort/topsort.py)
     - [wiggle_sort](sort/wiggle_sort.py)
+    - [counting_sort](sort/counting_sort.py)
 - [stack](stack)
     - [longest_abs_path](stack/longest_abs_path.py)
     - [simplify_path](stack/simplify_path.py)

sort/counting_sort.py

@@ -0,0 +1,46 @@
+def counting_sort(arr):
+	"""
+    Counting_sort
+	Sorting a array which has no element greater than k
+	Creating a new temp_arr,where temp_arr[i] contain the number of
+	element less than or equal to i in the arr	
+    Then placing the number i into a correct position in the result_arr
+	return the result_arr
+	Complexity: 0(n)
+	"""
+	
+	m = min(arr)
+	#in case there are negative elements, change the array to all positive element
+	different = 0
+	if m < 0:
+		#save the change, so that we can convert the array back to all positive number
+		different = -m
+		for i in range (len(arr)):
+			arr[i]+= -m
+	k = max(arr)
+	temp_arr = [0]*(k+1)
+	for i in range(0,len(arr)):
+		temp_arr[arr[i]] = temp_arr[arr[i]]+1
+	#temp_array[i] contain the times the number i appear in arr
+	
+	for i in range(1, k+1):
+		temp_arr[i] = temp_arr[i] + temp_arr[i-1]
+	#temp_array[i] contain the number of element less than or equal i in arr
+	
+	result_arr = [0]*len(arr)
+	#creating a result_arr an put the element in a correct positon
+	for i in range(len(arr)-1,-1,-1):
+		result_arr[temp_arr[arr[i]]-1] = arr[i]-different
+		temp_arr[arr[i]] = temp_arr[arr[i]]-1
+	
+	return result_arr 
+
+if __name__ == "__main__":
+	positive_array = [1,2,3,4,9,1,2,8,3,5,7,0,9,8,1,7,4,5]
+	negative_array = [-5,-6,-2,-3,-4,-5,0,-9,-2,-3,-8,-4]
+	x = counting_sort(positive_array)
+	y = counting_sort(negative_array)
+	print(x)
+	print(y)
+	
+