How would I search a range of ranged values using C#


How would I search a range of ranged values using C#



I have a list of values like this

1000, 20400 22200, 24444 

The ranges don't overlap.

What I want to do is have a c# function that can store (loaded values from db then cache it locally) a relatively large list of these values then have a method for finding if a supplied value is in any of the ranges?

Does this make sense?

Need the quickest solution




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1:



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You've specified values, but then talked about ranges..
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For just values, I'd use a HashSet<int>.


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For ranges it gets more complicated...


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Let us know if that's actually what you're after and I'll think about it more.


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If they are ranges, do you have any extra information about them? Do you know if they'll overlap or not? Are you just interested in the existence of a range, or do you need to find all the ranges that a value belongs to?.
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EDIT: With the edits to the question, Barry's answer is exactly right.


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Just sort (by lower bound is good enough) at initialization time and then do a binary search to find the range containing the value, or the lack thereof.. EDIT: I've found the code below in my answer to a similar question recently.. The ranges will need to be sorted beforehand - List<Range>.Sort will work fine assuming you have no overlap..
public class Range : IComparable<Range> {       private readonly int bottom; // Add properties for these if you want       private readonly int top;        public Range(int bottom, int top)       {              this.bottom = bottom;              this.top = top;       }        public int CompareTo(Range other)       {              if (bottom < other.bottom && top < other.top)              {                    return -1;              }              if (bottom > other.bottom && top > other.top)              {                    return 1;              }              if (bottom == other.bottom && top == other.top)              {                    return 0;              }              throw new ArgumentException("Incomparable values (overlapping)");       }        /// <summary>       /// Returns 0 if value is in the specified range;       /// less than 0 if value is above the range;       /// greater than 0 if value is below the range. 

/// </summary> public int CompareTo(int value) { if (value < bottom) { return 1; } if (value > top) { return -1; } return 0; } } // Just an existence search public static bool BinarySearch(IList<Range> ranges, int value) { int min = 0; int max = ranges.Count-1; while (min <= max) { int mid = (min + max) / 2; int comparison = ranges[mid].CompareTo(value); if (comparison == 0) { return true; } if (comparison < 0) { min = mid+1; } else if (comparison > 0) { max = mid-1; } } return false; }


2:


A binary search will do just fine.

Keep the list of ranges in sorted order, making sure that none of them intersect (if they do, merge them).

Then write a binary search which, rather than testing against a single value, tests against either end of the range when looking to choose above or below..


3:


I'd try the simplest option first, and optimize if that doesn't meet your needs..
class Range {    int Lower { get; set; }    int Upper { get; set; } }  List<Range>.FirstOrDefault(r => i >= r.Lower && i <= r.Upper); 


4:


Assuming your ranges don't overlap:.
-> Put all your range numbers in an array.. -> Sort your array.. -> Also keep a HashSet for your startvalues.. -> Now do a binary search on your number.

Two possiblities:. --> Array range left of (smaller then) your number is a start value: your number is in range.. --> Array range left of (smaller then) your number is not a start value: your number is not in range..


5:


Is this functionally what you're after? If so, and you just want it to be more performant, than change the foreach in the ValueRangeCollection to a binary search..

.
    public struct ValueRange      {         public int LowVal;         public int HiVal;         public bool Contains (int CandidateValue)         { return CandidateValue >= LowVal && CandidateValue <= HiVal; }         public ValueRange(int loVal, int hiVal)        {           LowVal = loVal;           HiVal = hiVal;        }    }      public class ValueRangeCollection: SortedList<int, ValueRange>      {          public bool Contains(int candValue)          {               foreach ( ValueRange valRng in Values)                 if (valRng.Contains(candValue)) return true;             return false;          }         public void Add(int loValue, int hiValue)         {             Add(loValue, new ValueRange(loValue, hiValue));         }     } 


6:


class Range {    public int Start { get; set; }    public int End { get; set; }     static Dictionary<int, Range> values;    static int[] arrToBinarySearchIn;    public static void BuildRanges(IEnumerable<Range> ranges) {          values = new Dictionary<int, Range>();         foreach (var item in ranges)             values[item.Start] = item;         arrToBinarySearchIn = values.Keys.ToArray();         Array.Sort(arrToBinarySearchIn);    }    public static Range GetRange(int value)    {        int searchIndex = Array.BinarySearch(arrToBinarySearchIn, value);        if (searchIndex < 0)            searchIndex = ~searchIndex - 1;        if (searchIndex < 0)            return null;        Range proposedRange = values[arrToBinarySearchIn[searchIndex]];        if (proposedRange.End >= value)            return proposedRange;        return null;    } } 


7:


class Ranges {     int[] starts = new[] { 1000, 22200 };     int[] ends = new[] { 20400, 24444 };      public int RangeIndex(int test)     {         int index = -1;          if (test >= starts[0] && test <= ends[ends.Length - 1])         {             index = Array.BinarySearch(ends, test);              if (index <= 0)             {                 index = ~index;                 if (starts[index] > test) index = -1;             }         }          return index;     } } 
Obviously, how you instantiate the class is up to you.

Maybe pass in a DataTable and construct the arrays from that..



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