[40 pt] In this problem, you are tasked with sorting a string in increasing order based on the number of occurrences of characters. If there is a tie, output them based on alphabetical order, e.g., 'a' before 'e'. You can assume that all the characters are lower-case letters (so a total of 26 possible types of characters). Below are some example inputs and the corresponding expected outputs. Inputl: "engineers" Output2: "girsnneee" Input2: "engineering" Output2: "rggiieeennn