In the above method we have to traverse the entire string every time for each of the character in set of ‘a’ to ‘z’.We can overcome this drawback by maintaining a character and filling it with number of the occurrence’s of all the characters in the string.Later we can construct the required sorted string from the character array.
Below is the implementation.

Sort the given string using character search : https://www.geeksforgeeks.org/sort-given-string-using-character-search/