/*
* Turn API to private - based on code review
*
* AddWordToTrieByOneCharATime
* function is designed to complete the following tasks:
* Add one word in the dictionary to Trie using recursive function
* Add one char a time by scanning a word from left to right.
*
* Tricky part is to set prefix neighbor in the process.
*
* @index
* @charArray
* @word -
* @neighbor - prefix neighbor, it is empty string if there is no prefix neighbor
*
* function return:
* Tuple<string, string> - string and its prefix neighbor
*/
private Tuple <string, string> addWordToTrieByOneCharATime(
int scanIndex,
char[] charArray,
string word,
string neighbour)
{
bool isEndOfString = scanIndex == charArray.Length;
if (isEndOfString)
{
IsWord = true;
PrefixNeighbor = word;
return(new Tuple <string, string>(PrefixNeighbor, neighbour));
}
char visiting = charArray[scanIndex];
if (!Children.ContainsKey(visiting))
{
Children[visiting] = new TrieWithPrefixNeighbor();
}
string updatedNeighbor = IsWord ? PrefixNeighbor : neighbour;
// update neighbor string - if IsInDictionary is true, then it is
// to set as a prefix neighbor
return(Children[visiting].addWordToTrieByOneCharATime(
scanIndex + 1,
charArray,
word,
updatedNeighbor));
}
/*
* study LINQ - GroupBy
* https://msdn.microsoft.com/en-us/library/bb534304(v=vs.110).aspx
*
* 1. Group string by first char, 26 variations from 'A', 'B', ..., 'Z'
* 2. For each group, sort strings by string's length in ascending order
* 3. For example, group of strings starting from char 'A',
* "A","AB","ACD"
* 4. benefit value is to add all chars' ascii value.
*/
static long Process(string[] dict)
{
var benefitValue = 0L;
var groupped = dict.GroupBy(x => x[0]);
// maximum 26 groups, 'A','B', ..., 'Z'
foreach (var group in groupped)
{
// sort by string's length in ascending order
var sortedStrings = group.OrderBy(x => x.Length);
var trie = new TrieWithPrefixNeighbor();
var banned = new HashSet <string>();
var stack = new Stack <Tuple <string, string> >();
foreach (var word in sortedStrings)
{
stack.Push(trie.AddWordToTrie(word, ""));
}
// Enumerate the stack, the longest string will be iterated first.
// Maximum independent set is kind of greedy as well.
foreach (var tuple in stack)
{
if (!banned.Contains(tuple.Item1))
{
benefitValue += tuple.Item1.ToCharArray().Aggregate(0L, (val, next) => val + (long)next);
banned.Add(tuple.Item2);
}
}
}
return(benefitValue);
}
