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Python Program for Counting Sort
• Last Updated : 30 Dec, 2020

Counting sort is a sorting technique based on keys between a specific range. It works by counting the number of objects having distinct key values (kind of hashing). Then doing some arithmetic to calculate the position of each object in the output sequence.

 `# 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 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 ``=` `"geeksforgeeks"``ans ``=` `countSort(arr)``print` `"Sorted character array is %s"`  `%``("".join(ans))`` ` `# This code is contributed by Nikhil Kumar Singh`

Output:

```Sorted character array is eeeefggkkorss
```

Please refer complete article on Counting Sort for more details!

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