Given a list of words, provide a method that takes two words and returns the shortest distance (in words) between those two words in the provided text.

WordDistanceFinder.swift

/* The following was a coding question given during an interview for LinkedIn in March, 2017 */

/* This class will be given a list of words (such as might be tokenized
 * from a paragraph of text), and will provide a method that takes two
 * words and returns the shortest distance (in words) between those two
 * words in the provided text.
 * Example:
 *   WordDistanceFinder finder = new WordDistanceFinder(Arrays.asList("the", "quick", "brown", "fox", "quick"));
 *   assert(finder.distance("fox", "the") == 3);
 *   assert(finder.distance("quick", "fox") == 1);
 *
 * "quick" appears twice in the input. There are two possible distance values for "quick" and "fox":
 *     (3 - 1) = 2 and (4 - 3) = 1.
 * Since we have to return the shortest distance between the two words we return 1.
 */
 
/* And now my answer in Swift 3 */

import Foundation

class WordDistanceFinder
{
    var words : [String]?
    
    init(array : [String])
    {
        words = array
    }
    
    func distance(_ word1: String, _ word2: String) -> Int
    {
        var distance = 99999
        
        // dereference optional
        if let words = words
        {
            // find indexes for word1 matches in the word array
            let arrayA = words.enumerated().filter {
                $0.element.contains(word1)
                }.map{$0.offset}

            // and word2, too
            let arrayB = words.enumerated().filter {
                $0.element.contains(word2)
                }.map{$0.offset}
            
            // now use binary search to find element with closest value in the index arrays
            var i = 0
            var j = 0
            var finished = false
            
            repeat {
                if arrayA[i] == arrayB[j]
                {
                    return 0
                }
                
                let diff = abs(arrayA[i] - arrayB[j])
                
                distance = min(distance, diff)

                if arrayA[i] > arrayB[j]
                {
                    j = j+1
                } else {
                    i = i+1
                }
                
                if(j >= arrayB.count)
                {
                    finished = true
                }
                
                if(i >= arrayA.count)
                {
                    finished = true
                }
            } while (finished == false)
                
        }
        
        return distance;
    }
}