DZone Java Code Challenge: Chemical Symbol Naming-Part One
Introduction
This is my contribution to the DZone Java Code Challenge: Chemical Symbol Naming-Part One. See their [Website] (https://dzone.com/articles/java-code-challenge-chemical-symbol-naming-part-on) for the rules of this code challenge. The project can be build using Apache Maven. The Unit Tests are implemented with help of JUnit 4. There are no other dependencies.
Primary Challenge: Validator
The Validator Implementation can be found in the class de.ender74.dzcode.ch01.SymbolValidator. The Unit Tests are implemented in the class de.ender74.dzcode.ch01.test.SymbolValidatorTest. The Testcases are taken from the description of the challenge. There is one test per rule example.
The implementation can be found in the validate method. First the input is normalized (trimmed & changed to lowercase). Then the characters of the symbol are iterated (for-each) and then matched against the elementName. For each character, the first possible matching index in the elementName is used. The matching starts at the matched index for the previous char +1. If no match can be found for one char, the symbol is invalid and false returned. If all chars can be matched, the symbol is valid.
The implementation works for arbitrary symbollength, not just two as in the challenge.
Bonus Challenge 1: Find symbol that is first in alphabetical order
This Challenge is implemented in the class de.ender74.dzcode.ch01.SymbolCreatorFirstAlph and tested in the class de.ender74.dzcode.ch01.test.SymbolCreatorFirstAlphTest.
The implementation does use the helper function indexOfLowestChar. This helper function finds the first index of the character which is the first in alphabetical order within a given range [start, end] of a string.
This helper function is used by the main method createSymbol. The implementation consists of a loop with n-iterations (n being the length of the symbol, e.g. two for this challenge). For each iteration the indexOfLowestChar function is called to find the alphabetically lowest char in the remaining elementName string. each index must be strictly greater than the found index for the previous iteration. Further the index must be less than the length of the elementName minus the number of left iterations.
The implementation works for arbitrary symbollength, not just two as in the challenge.
Bonus Challenge 2: Find maximum number of distinct symbols for given elementName
This Challenge is implemented in the class de.ender74.dzcode.ch01.DistinctSymbolCounter and tested in the class de.ender74.dzcode.ch01.test.DistinctSymbolCounterTest.
The implementation is done with brute force. There are two nested iterations over the given elementName. Each possible symbol is constructed and added to an HashSet. The HashSet takes care, that there is a distinct collections for all possible symbols when the algorithm is finished. The size of this set is the required result.
For clarity this implementation works only for symbols of length 2. To make it work with arbitrary symbollength, the implementation would probably be way more complex and less understandable.