Algorithm for text selection intersection

I have a website that allows multiple users to highlight multiple parts of a html document (mostly text).

Each highlight is marked by the start, character position, length and user id.

I need to find 开发者_Python百科out the most highlighted sections (most overlapped sections), however different users might not have the same start and end position. What's the best way to implement such feature? preferably in c#

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Put all the users' begin and end selections in a list, sorted. Start at the top of the list and increment a counter for each begin point you find, decrement for each end point you find. The highest value of the counter is the start of your most highlighted / most overlapped section of text. The next item in the list is the end of that selection.

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This should convert your data into the structure needed for dthorpe algorithm. If I had more time, I could probably Linq-ify the rest.

UPDATE: Ok, Now complete (if still untested....) UPDATE2: Now, actually tested & Working!

// Existing data structure
class StartLen
{
    public int Start {get; set;}
    public int Len   {get; set;}
    public string UserId {get; set;}
}

// Needed data struct
class StartEnd
{
    public int Pos {get; set;}
    public bool IsStart {get; set;}
}

class Segment
{
    public int Start { get; set; }
    public int End { get; set; }
    public int Count { get; set; }
}    

int count = 0, lastStart = -1;   // next rev, I figure a way to get rid of these. 

 // this can't be a lambda, it has to be a real function
IEnumerable<StartEnd> SplitSelection(StartLen sl)
 {  
    yield return new StartEnd() {Pos = sl.Start, IsStart = true} ; 
    yield return new StartEnd() {Pos = sl.Start+sl.Len -1 , IsStart = false} ; 
 }

List<StartLen> startLen = new List<StartLen>();
// we fill it with data for testing
// pretending to be the real data
startLen.Add(new StartLen() { Start=10, Len=10, UserId="abc123" });
startLen.Add(new StartLen() { Start=15, Len=10, UserId="xyz321" });

 var mostSelected  =  
    startLen.SelectMany<StartLen, StartEnd>(SplitSelection) 
        .OrderBy(se=>se.Pos) 
        .Select(se=>
        { 
            if (se.IsStart) 
            { 
                lastStart = se.Pos; 
                count++; 
            } 
            else 
            { 
                count--; 
                if (lastStart > 0) 
                { 
                    var seg = new Segment  
                        { Start = lastStart, End = se.Pos, Count = count }; 
                    lastStart = -1; 
                    return seg;
                } 
            } 
            // Garbage, cuz I need to return something 
            return new Segment { Start = 0, End = 0, Count = -1 };  
        }) 
       .OrderByDescending(seg => seg.Count) 
       .First(); 

// mostSelected  holds Start & End positions
}