Optimize the cost of concatenation of all these strings into one big string.

You have n strings with their lengths. You are given an add(string s1,string s2) which would concatenate the string s2 with s1 and return s3. Optimize the cost of concatenation of all these strings into one big string.
Eg: 1,5,2 are the lengths of given strings.
1+5=6
6+2=8
total cost=14 can you Optimize this total cost?

Source : Sent by a reader named rahul.

Design Data Structure For Students-Courses Realtionship

In a university, students can enroll in different courses. A student may enroll for more than one course. Both students and courses can be identified by IDs given to them. Design a data structure to store students, courses, and the student-course relationships. You can use arrays, lists, stacks, trees, graphs, etc. or come up with your own data structures. Give the running times, in Big O notation, for the following operations for your data structure and justify the answers: a) Return all students in a list. b) Return all courses in a list. c) Return all courses in a list for a given student. d) Return all students in a list for a given course.

Given a list of Tagalog words as a String[], return the same list in Tagalog alphabetical order

A Reader send me this problem . Thanks to Him for this intersteing Problem. so i am going to posting here.

In the first half of the 20th century, around the time that Tagalog became the national language of the Philippines, a standardized alphabet was introduced to be used in Tagalog school books (since then, the national language has changed to a hybrid "Pilipino" language, as Tagalog is only one of several major languages spoken in the Philippines).

Tagalog's 20-letter alphabet is as follows:

a b k d e g h i l m n ng o p r s t u w y

Note that not all letters used in English are present, 'k' is the third letter, and 'ng' is a single letter that comes between 'n' and 'o'.

You are compiling a Tagalog dictionary, and for people to be able to find words in it, the words need to be sorted in alphabetical order with reference to the Tagalog alphabet. Given a list of Tagalog words as a String[], return the same list in Tagalog alphabetical order

1)


{"ang","ano","anim","alak","alam","alab"}

Returns: {"alab", "alak", "alam", "anim", "ano", "ang" }

A few "A" words that are alphabetically close together.
2)


{"siya","niya","kaniya","ikaw","ito","iyon"}

Returns: {"kaniya", "ikaw", "ito", "iyon", "niya", "siya" }

Common Tagalog pronouns.
3)


{"kaba","baka","naba","ngipin","nipin"}

Returns: {"baka", "kaba", "naba", "nipin", "ngipin" }