Added counting sort in python

sorts/countingsort.py

@@ -0,0 +1,41 @@
+# Python program for counting sort
+ 
+# This is the main function that sort the given string arr[] in
+# in the 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 inidividul
+    # 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 = "thisisthestring"
+ans = countSort(arr)
+print ("Sorted string array is %s"  %("".join(ans)))