My one test case is not working in this program

#1
#2

In case the length of the given string is 1, your code will output 1, which is wrong. To rectify this, change this initialization :

char ch=‘1’;

to

char ch = s.charAt(0);

Your approach is totally correct but as a suggestion, consider using a HashMap/frequency array for frequency-related questions to reduce the time complexity of your code to O(n).