Write a function that takes two parameters:
- a String representing the contents of a text document
- an integer providing the number of items to return
Implement the function such that it returns a list of Strings ordered by word frequency, the most frequently occurring word first. Use your best judgment to decide how words are separated. Implement this function as you would for a production / commercial system
You may use any standard data structures. You may use Objective-C as your programming language.
Performance Constraints: Your solution must run in O(n) time where n is the number of characters in the document. Please provide reasoning on how the solution obeys the O(n) constraint.
There are two implementations of the sortedWordFrequency method.
I am excited about Swift, so I've done both implementations twice. The first time, using swift, and the same methods again using Objective-c.
This is the Ojvective-c version. View Swift Version
Both methods take two parameters:
- a String representing the contents of a text document
- an integer providing the number of items to return
Both methods return a sorted array of dictionary objects that contains the Strings ordered by word frequency, the most frequently occurring word first.
The first, sortedWordFrequency uses an enumerator to iterate over the string and add words to a NSCounted set.
The second, fasterSortedWordFrequency splits the words into an array using NSMutableCharacterSet as separators, and then adds the array to the NSCounted set all at once, eliminating a high level enumeration.
While the second approach is faster, words wrapped in single quotes get added with the quotes, and phrases with single quotes may create words with a leading or trailing single quote. I'm sure this could be over come given a little extra time. In many cases this may be acceptable, so I'm leaving both methods in the class for additional exploration.
You can run the application to see it display the top 20 words from the textView. There is also a suite of tests that verify functionality.
I've tried to meet the linear time constraint by using data structures built specifically for this type of task, and limiting iterations over the data. I've also prepared tests to measure the time it takes to complete the task as the text input string gets larger. Here's some data for the two methods. All of my measurement was done using Swift.
| Method | Time for: | 191,250 Chrs | 382,500 Chrs | 765,000 Chrs | 1,530,000 Chrs | 3,060,000 Chrs |
|---|---|---|---|---|---|---|
| sortedWordFrequency | 1.002 | 1.99 | 3.914 | 8.02 | 15.985 | |
| fasterSortedWordFrequency | 0.38 | 0.756 | 1.459 | 3.013 | 5.991 |
Please let me know if there is anything else that I can do.
Best
Tim