Create countingsort.py

Python/countingsort.py

@@ -0,0 +1,43 @@
+# Python program for counting sort
+
+# The main function that sort the given string arr[] in 
+# alphabetical order
+def countSort(arr):
+
+	# The output character array that will have sorted arr
+	output = [0 for i in range(256)]
+
+	# Create a count array to store count of individual
+	# characters and initialize count array as 0
+	count = [0 for i in range(256)]
+
+	# For storing the resulting answer since the 
+	# string is immutable
+	ans = ["" for _ in arr]
+
+	# Store count of each character
+	for i in arr:
+		count[ord(i)] += 1
+
+	# Change count[i] so that count[i] now contains actual
+	# position of this character in output array
+	for i in range(256):
+		count[i] += count[i-1]
+
+	# Build the output character array
+	for i in range(len(arr)):
+		output[count[ord(arr[i])]-1] = arr[i]
+		count[ord(arr[i])] -= 1
+
+	# Copy the output array to arr, so that arr now
+	# contains sorted characters
+	for i in range(len(arr)):
+		ans[i] = output[i]
+	return ans 
+
+# Driver program to test above function
+arr = "geeksforgeeks"
+ans = countSort(arr)
+print ("Sorted character array is %s" %("".join(ans)))
+
+# This code is contributed by Nikhil Kumar Singh