An Example of a (LINQ) Approach to Solve Recurring Problems

Introduction

Most of the time, we think about LINQ in terms of querying the data model.

However, it can give a set of alternative solutions to problems that we just drill in a very primitive and basic way. That is because it is used to perform operations on generics of any data type.

Problem

One task I handled lately was to find the gap in a series of numbers. Let us discuss the first solution that comes into one's mind when one approaches the task at the first stage.

First Solution

To be able to follow the discussion, create a .NET console application and copy the below code inside program.cs class file:

//################
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;

namespace NumberSeriesGapFinder
{
    class Program
    {
        static void Main(string[] args)
        {
            string inputNumbers;
          
            Console.WriteLine("Enter a set of numbers comma separated, 
                               make sure there is no gap in the set");
            Console.WriteLine("for example:1,2,4,5 has a gap while 6,7,8,9 has no gap");

            inputNumbers = Console.ReadLine();
            try
            {
                CheckGap(inputNumbers);
            }
            catch(Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadLine();
        }
       static void CheckGap(string inputNumbers)
        {
            bool GapExist = false;
            List<string> SetElements;
            SetElements = inputNumbers.Split(",".ToCharArray()[0]).ToList();

            for (int i=0;i<SetElements.Count-1;i++)//here, we are excluding the last element 
                                                   //if the series ends at 8 
                                                   //it will not contain 9
            {
                if(!SetElements.Contains((int.Parse(SetElements.ElementAt(i))+1).ToString()))
                {
                    GapExist = true;
                    break;
                }
            }
            if(GapExist)
            {
                Console.WriteLine("Gap Exist in the series, please try again");
               inputNumbers = Console.ReadLine();
                CheckGap(inputNumbers);
            }
            else
            {
                Console.WriteLine("The series entered has no gaps");
            }
        }
    }
}
//####################

The code above is a very basic solution for the problem, but there are two drawbacks after a deeper look.

1. It works in a nested loop manner which will keep the memory busy holding loop index and scanning the whole series against each element.
2. The numbers should be in ascending order since we do not know the element with highest value. This element should be excluded from the check since it is the upper boundary of the series.

Second Solution

Place the following code below method discussed in solution 1:

//##################
static void CheckGap2(string inputNumbers)
        {        
            bool GapExist = false;
            int MaxElement;

            List<string> SetElements,SetElementsMissingSubSequent;
            SetElements = inputNumbers.Split(",".ToCharArray()[0]).ToList();
            MaxElement = (from x in SetElements select int.Parse(x)).Max();

            SetElementsMissingSubSequent = (from x in SetElements.Where
                                           (w=>int.Parse(w)<MaxElement)
                                           join y in SetElements
                                           on (int.Parse(x)+1) equals (int.Parse(y))
                                           into lj 
                                           from ljr in lj.DefaultIfEmpty()
                                                //left join
                                                //is a relational algebra operator that 
                                                //finds out the  elements between 
                                                //two tuples a and b
                                                //which hold the same value for
                                                //join column a as well as the elements in a 
                                                //that have values for the 
                                                //join column that do not exist in b 
                                           where ljr==null
                                           select ljr
                                          ).ToList();
            GapExist = SetElementsMissingSubSequent.Count > 0;

            if (GapExist)
            {
                Console.WriteLine("Gap Exist in the series, please try again");
                inputNumbers = Console.ReadLine();
                CheckGap2(inputNumbers);
            }
            else
            {
                Console.WriteLine("The series entered has no gaps");
            }
        }
//##########

Notice that we have used LINQ to

1. perform left join operator between the series and itself (you can refresh your information about left using the comments inside the method). Any number where its subsequent does not exist will satisfy the where condition.
2. Select the element with maximum value of the element. The series does not have to be entered in order this way.

Now call the method from main method and try.

Conclusion

Most of the time, we think about LINQ in terms of querying the data model .

However, it can give a set of alternative solutions to problems that we just drill in a very primitive and basic way. That is because it is used to perform operations on generics of any data type.

History

• 6^th March, 2021: Initial version