Counting Sort

class Solution:
    #Function to arrange all letters of a string in lexicographical 
    #order using Counting Sort.
    def countSort(self,arr):
        temp=[0]*26
        ans=''
        for i in arr:
            temp[ord(i)-97]+=1
        for i in range(26):
            if temp[i]!=0:
                char=chr(97+i)
                ans+=char*temp[i]
        return ans