khizar/phonenumberencoding

Task description

Attention: Please follow these instructions super accurately.

• Develop the solution yourself. Do not try to find a shortcut by using the web.

• Develop the solution in Java using maven as build tool.

• The core of the solution should be written without any add-ons to the core of the programming language. Use only the defined language standard (e.g. you can use all features that you find in a standard Sun JDK). This means that you can use external libraries, but your program should still produce the wanted solutions after removing those parts. For example, if you would decide to use a logging library then your program would still work correctly after removing all parts that use the logging library. You can also use JUnit.

• Optimize for speed of development and quality of development. Do not optimize for runtime execution speed. The problem is small and you can afford to waste a few milli seconds. It is better to focus on getting a working solution faster.

• Deliver your result in the best professional quality you can produce. Polish your solution. Make a master piece out of it. It is part of this task to compare what different people consider to be a professional quality solution.

First read through the whole of it in order to get an overview. Concentrate on the details only upon second reading.

The following mapping from letters to digits is given:

E | J N Q | R W X | D S Y | F T | A M | C I V | B K U | L O P | G H Z e | j n q | r w x | d s y | f t | a m | c i v | b k u | l o p | g h z 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

We want to use this mapping for encoding telephone numbers by words, so that it becomes easier to remember the numbers.

Functional requirements

Your task is writing a program that finds, for a given phone number, all possible encodings by words, and prints them. A phone number is an arbitrary(!) string of dashes - , slashes / and digits. The dashes and slashes will not be encoded. The words are taken from a dictionary which is given as an alphabetically sorted ASCII file (one word per line).

[NOTE: The dictionary is in German and contains umlaut characters encoded as double-quotes. The double-quotes should be ignored. EG.]

Only exactly each encoding that is possible from this dictionary and that matches the phone number exactly shall be printed. Thus, possibly nothing is printed at all. The words in the dictionary contain letters (capital or small, but the difference is ignored in the sorting), dashes

• and double quotes " . For the encoding only the letters are used, but the words must be printed in exactly the form given in the dictionary. Leading non-letters do not occur in the dictionary.

Encodings of phone numbers can consist of a single word or of multiple words separated by spaces. The encodings are built word by word from left to right. If and only if at a particular point no word at all from the dictionary can be inserted, a single digit from the phone number can be copied to the encoding instead. Two subsequent digits are never allowed, though. To put it differently: In a partial encoding that currently covers k digits, digit k+1 is encoded by itself if and only if, first, digit k was not encoded by a digit and, second, there is no word in the dictionary that can be used in the encoding starting at digit k+1.

Your program must work on a series of phone numbers; for each encoding that it finds, it must print the phone number followed by a colon, a single(!) space, and the encoding on one line; trailing spaces are not allowed. All remaining ambiguities in this specification will be resolved by the following example. (Still remaining ambiguities are intended degrees of freedom.)

Sample dictionary:

an blau Bo" Boot bo"s da Fee fern Fest fort je jemand mir Mix Mixer Name neu o"d Ort so Tor Torf Wasser

Sample phone number list:

112 5624-82 4824 0721/608-4067 10/783--5 1078-913-5 381482 04824

Corresponding correct program output (on screen): 5624-82: mir Tor 5624-82: Mix Tor 4824: Torf 4824: fort 4824: Tor 4 10/783--5: neu o"d 5 10/783--5: je bo"s 5 10/783--5: je Bo" da 381482: so 1 Tor 04824: 0 Torf 04824: 0 fort 04824: 0 Tor 4

Any other output would be wrong (except for different ordering of the lines).

Wrong outputs for the above example would be e.g.

562482: Mix Tor, because the formatting of the phone number is incorrect,

10/783--5: je bos 5, because the formatting of the second word is incorrect,

4824: 4 Ort, because in place of the first digit the words Torf, fort, Tor could be used,

1078-913-5: je Bo" 9 1 da , since there are two subsequent digits in the encoding,

04824: 0 Tor , because the encoding does not cover the whole phone number, and

5624-82: mir Torf , because the encoding is longer than the phone number.

Quantitative requirements

Length of the individual words in the dictionary: 50 characters maximum. Number of words in the dictionary: 75000 maximum Length of the phone numbers: 50 characters maximum. Number of entries in the phone number file: unlimited.

Quality requirements

Work as carefully as you can as a professional software engineer and deliver a correspondingly high grade program. Specifically, thoroughly comment your source code (design ideas etc.).

The focus during program construction shall be on correctness. Generate exactly the right output format right from the start. Do not generate additional output. We will automatically test your program with hundreds of thousands of phone numbers and it should not make a single mistake, if possible -- in particular it must not crash. Take youself as much time as is required to ensure correctness.

Your program must be run time efficient in so far that it analyzes only a very small fraction of all dictionary entries in each word appending step. It should also be memory efficient in that it does not use 75000 times 50 bytes for storing the dictionary if that contains many much shorter words. The dictionary must be read into main memory entirely, but you must not do the same with the phone number file, as that may be arbitrarily large.

Your program need not be robust against incorrect formats of the dictionary file or the phone number file.

A large dictionary, which you can use for testing purposes, is available at dictionary.txt.