Arsalan’s Musings

Problem: Given a range of integers, count the number of primes. Also list the prime numbers in the range.

using System;

namespace SolvingSmallProblems
{
    public class Program
    {
        static void Main(string[] args)
        {
            int defaultLowNum = 1;
            int defaultHighNum = 50;
            int lowNum, highNum;
            PrimeNumberPuzzles prime = new PrimeNumberPuzzles();

            Console.WriteLine("PRIME NUMBER COUNT PROGRAM");
            Console.WriteLine();
            Console.WriteLine("Please enter start number");
            try
            {
                lowNum =
                Convert.ToInt32(Console.ReadLine());
            }
            catch (Exception)
            {
                lowNum = defaultLowNum;
            }

            Console.WriteLine("Please enter end number");
            try
            {
                highNum = Convert.ToInt32(Console.ReadLine());
            }
            catch (Exception)
            {
                highNum = defaultHighNum;
            }

            if (lowNum < 1)
            {
                lowNum = defaultLowNum;
            }
            if (highNum < lowNum)
            {
                highNum = defaultHighNum;
            }

            int totalPrimes = prime.CountPrimes(lowNum, highNum);
            Console.WriteLine();
            Console.WriteLine("Total number of prime numers between " +
                lowNum.ToString() + " and " + highNum.ToString() +
                " is " + totalPrimes + ".");
            Console.ReadKey();
        }
    }

    public class PrimeNumberPuzzles
    {
        public int CountPrimes(int low, int high)
        {
            int count = 0;
            for (int num = low; num <= high; num++)
            {
                if (IsPrime(num))
                {
                    Console.Write(num + " ");
                    count++;
                }
            }
            return count;
        }

        bool IsPrime(int num)
        {
            bool isNumPrime = true;
            if ( num == 2)
            {
                return true;
            }
            else if (num == 1)
            {
                return false;
             }
            else if (num < 1)
            {
                throw new Exception("Invalid number!");
            }
            else
            {
                int remainder;
                for (int test = 2; test < num - 1; test++)
                {
                    remainder = num % test;
                    if (remainder == 0)
                    {
                        isNumPrime = false;
                    }
                }
                return isNumPrime;
            }
        }
    }
}

Problem 1 Description: Reverse a string such that “a cat has paws” becomes “paws has cat a”.

Problem 2 Description: Remove a set of characters from a given string.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace StringManipulationProblems
{
    class Program
    {
        const string DEFAULT_COMMAND = "ReverseString";
        const string DEFAULT_ARGUMENT_1 = "messages that have been in Spam more than 30 days will be automatically deleted";
        const string DEFAULT_ARGUMENT_2 = "aioeu";
        static void Main(string[] args)
        {
            string commandName;
            string commandArg1;
            string commandArg2;
            if (args.Length < 1)
            {
                commandName = DEFAULT_COMMAND;
                commandArg1 = DEFAULT_ARGUMENT_1;
                commandArg2 = DEFAULT_ARGUMENT_2;
            }
            else if (args.Length == 1)
            {
                commandName = args[0];
                commandArg1 = DEFAULT_ARGUMENT_1;
                commandArg2 = "aioeu";
            }
            else if (args.Length == 2)
            {
                commandName = args[0];
                commandArg1 = args[1];
                commandArg2 = "aioeu";
            }
            else
            {
                commandName = args[0];
                commandArg1 = args[1];
                commandArg2 = args[2];
            }

            string result = String.Empty;
            StringPuzzles puzzles = new StringPuzzles();

            switch (commandName)
            {
                case "ReverseString":
                    if (commandArg1.Equals(DEFAULT_ARGUMENT_1))
                    {
                        Console.Out.Write("No string argument provided. Using default string: ");
                        Console.WriteLine(DEFAULT_ARGUMENT_1);

                    }
                    Console.Out.WriteLine("About to call method " + commandName);
                    result = puzzles.ReverseString(commandArg1);
                    break;

                case "RemoveChars":
                    if (commandArg1.Equals(DEFAULT_ARGUMENT_1))
                    {
                        Console.Out.Write("No string argument provided. Using default string: ");
                        Console.WriteLine(DEFAULT_ARGUMENT_1);

                    }
                    Console.Out.WriteLine("About to call method " + commandName);
                    result = puzzles.RemoveChars(commandArg1, commandArg2);
                    break;

                default:
                    Console.Out.WriteLine("Incorrect command! Please try again.");
                    break;
            }

            Console.Out.WriteLine("The original string was:");
            Console.Out.WriteLine(commandArg1);
            Console.Out.WriteLine("The modified string is:");
            Console.Out.WriteLine(result);
            Console.Out.WriteLine("Please press ENTER to continue...");
            Console.In.ReadLine();
        }
    }

    class StringPuzzles
    {

        public string ReverseString(string inputString)
        {
            List<string> wordList;
            StringBuilder reversedString = new StringBuilder();

            wordList =  new List<string>(inputString.Split(' '));
            for (int i = wordList.Count - 1; i >= 0; i--)
            {
                reversedString.Append(wordList[i] + " ");
            }

            return reversedString.ToString();
        }

        public string RemoveChars(string str, string remove)
        {
            List<char> toDelete = new List</char><char>();
            StringBuilder deletedStr = new StringBuilder();

            // Create a list of characters to delete from string
            toDelete.AddRange(remove.ToCharArray());

            // Create string with specified characters removed
            foreach (char c in str.ToCharArray())
            {
                if (!(toDelete.Contains(c)))
                {
                    deletedStr.Append(c);
                }
            }

            return deletedStr.ToString();
        }
    }
}

I propose the following problem. Take the number of columns and a series of numbers between 10 and 99 as input and create a zig-zag pattern on console output. The output should be centered so that it fills an 80 char wide screen. For example,

prompt>ZigZag 3 12 45 78 48 34 67 90 23 72 67 34 56 17 32 88

will give the following output:

12
                                                             45
                                                                                                                               78
                                                            48
34
                                                            67
                                                                                                                               90
                                                            23
72 
                                                             67 
                                                                                                                               34
                                                             56
17
                                                             32
                                                                                                                               88

———————————————————————————

I will try to write C# code to solve this problem below within a day or two.

This is a variation to the problem/solution posted on Ali Abbas Rizvi’s blog. I wanted to allow the user to enter matrix size for each run and to get a view of a randomly generated matrix in addition to all the sums for rows and columns. I also wanted to create a design that would lend itself favorably to adding new functionality. As an example, two methods (AddAllRows and AddAllColumns) have been added to the SquareMatrix class.

// Problem: Given a matrix, add rows and columns
// Author: Ahmed Arsalan
// (c) 2008. Please cite source if used in your presentation.

using System;
using System.Linq;
using System.Text;

namespace SolvingSmallProblems
{
    class Program
    {
        static void Main(string[] args)
        {
            SquareMatrix aMatrix;
            int matrixSize;

            Console.Out.WriteLine("Please enter matrix size (e.g. 10):");
            try
            {
                matrixSize = Int32.Parse(Console.In.ReadLine().Trim());
            }
            catch (Exception)
            {
                Console.Out.WriteLine("Please entger a valid integer.");
                throw new Exception("Invalid size entered!");
            }
            Console.Out.WriteLine("The randomly generated matrix looks like this:");

            aMatrix = new SquareMatrix(matrixSize);

            for (int underline = 0; underline < matrixSize; underline++)
            {
                Console.Out.Write("____");
            }
            aMatrix.Show();

            Console.Out.WriteLine("Press ENTER to generate sums...");
            Console.In.ReadLine();

            // display sums
            long [] rowSums = new long [matrixSize];
            long [] columnSums = new long [matrixSize];
            for (int rowOrColumn = 0; rowOrColumn < matrixSize; rowOrColumn++)
            {
                rowSums[rowOrColumn] = aMatrix.AddRow(rowOrColumn);
                columnSums[rowOrColumn] = aMatrix.AddColumn(rowOrColumn);

                Console.Out.WriteLine (String.Format ("The sum of row {0} is {1}, " +
                       "and the sum of column {2} is {3}. ", rowOrColumn,
                       rowSums[rowOrColumn], rowOrColumn, columnSums[rowOrColumn]));
            }

            Console.Out.WriteLine (String.Format ("The MAX of all rows is {0}, " +
                  "and the MAX of all columns is {1}", rowSums.Max(), columnSums.Max()));
            Console.In.ReadLine();
        }
    }

    class SquareMatrix
    {
        # region ------------------------ Instance Variables ------------------------
        private const int DEFAULT_MATRIX_SIZE = 10;
        int[,] matrix;
        Random randomNumber;
        int selectedMatrixSize;
        #endregion

        #region ------------------------ Constructors ------------------------
        public SquareMatrix() :this(DEFAULT_MATRIX_SIZE)
        {
            // use default size
        }

        public SquareMatrix(int matrixSize)
        {
            randomNumber = new Random(99);
            selectedMatrixSize = matrixSize;

            matrix = new int[matrixSize, matrixSize];
            for (int row = 0; row < matrixSize; row++)
            {
                for (int column = 0; column < matrixSize; column++)
                {
                    try
                    {
                        matrix[row, column] = RandomNumber; // random # between 1 and 99
                    }
                    catch (Exception)
                    {
                        Console.out.WriteLine ("Error generating random number!");
                        throw new Exception ("Error generating random number.");
                    }
                }
            }
        }
        #endregion

        # region ------------------------ Public Properties ------------------------
        public int RandomNumber
        {
            get
            {
                return randomNumber.Next(1, 99);
            }
        }
        #endregion

        #region ------------------------ Public Methods ------------------------
        public void Show()
        {
            for (int row = 0; row < selectedMatrixSize; row++);

                for (int column = 0; column < selectedMatrixSize; column++)
                {
                    Console.Out.Write(matrix[row, column]);
                    Console.Out.Write("  ");
                }

                Console.Out.WriteLine();
            }
        }

        public long AddRow(int rowNumber)
        {
            long addedRow = 0;
            for (int column = 0; column < selectedMatrixSize; column++)
            {
                addedRow += matrix[rowNumber, column];
            }

            return addedRow;

        }

        public long AddColumn(int columnNumber)
        {
            long addedColumn = 0;
            for (int row = 0; row < selectedMatrixSize; row++)
            {
                addedColumn += matrix[row, columnNumber];
            }

            return addedColumn;

        }

        public long AddAllRows()
        {
            long addedAllRows = 0;
            for (int row = 0; row < selectedMatrixSize; row++)
            {
                addedAllRows += AddRow(row);
            }
            return addedAllRows;
        }

        public long AddAllColumns()
        {
            long addedAllColumns = 0;
            for (int column = 0; column < selectedMatrixSize; column++)
            {
                addedAllColumns += AddColumn(column);
            }
            return addedAllColumns;
        }
        #endregion

    }
}

When I decided to start a blog to post source code for small projects, I needed a blogging platform that would make posting source code with keyword highlights, line numbers, and proper indentation a snap. After a bit of search and general disappointment with blogging systems, I came across the wonderful feature in WordPress that let’s you post beautifully styled source code simply by enclosing the code inside the SourceCode tag! And that was all I had to do! Brilliant!

The only caveat I found so far is that the view seems fixed in width. So you have to choose a theme that gives you more space in the main text area. If a line in your code is longer than what the template allows, you will get a horizontal scroll bar. However, if you scroll right to see the overflowing code, you will notice that the alternating background color scheme does not apply there. Clearly a bug and a big disappointment. I hope some body at WordPress sees this post and removes that defect. This is still the best and easiest way to date to showcase your source code in a blog.

Here is the FAQ for WordPress.

Happy coding!

This is a solution for the problem posted by Ali Abbas Rizvi here. Command line arguments are method name (e.g. AddMinutes), start time (e.g. 9:24AM), and minutes to add (e.g. 18). The result will be the new time after addminutes in the same time format.

using System;
using System.Text.RegularExpressions;
using System.Collections.Specialized;

namespace SolvingSmallProblems
{
    class Program
    {
        static void Main(string[] args)
        {
            TimeConversions timeConv = new TimeConversions();

            string commandName;
            string baseTime;
            string incrementalTime;
            string output;
            if (args.GetLength(0) == 3)
            {
                commandName = args[0];
                baseTime = args[1];
                incrementalTime = args[2];

                switch (commandName.ToUpper())
                {

                    case ("ADDMINUTES"):
                        output = timeConv.AddMinutes(baseTime, Int32.Parse(incrementalTime));
                        Console.Out.WriteLine(output);
                        Console.Out.Flush();
                        break;
                }
            }
            else
            {
                throw new Exception("Incorrect number of arguments: 2 expected...");
            }

        }      

    }

    class TimeConversions
    {
        private StringCollection meridiemValidValues;
        public StringCollection methodsAvailable;

        public TimeConversions()
        {
            meridiemValidValues = new StringCollection();
            meridiemValidValues.Add("AM");
            meridiemValidValues.Add("PM");

            methodsAvailable = new StringCollection();
            methodsAvailable.Add("AddMinutes");
        }

        public string AddMinutes(string time, int minutesToAdd)
        {
            long convertedTime = ConvertTimeToMinutes(time);
            string finalTime = ConvertMinutesToTime(convertedTime + minutesToAdd);
            return finalTime;
        }

        private string ConvertMinutesToTime(long minutes)
        {
            long calculatingHours;
            long calculatingMinutes;
            string calculatingMeridiem;

            calculatingMinutes = minutes % 60;
            // Rolling over hours for a 24-hour clock
            calculatingHours = (minutes / 60) % 24;

            if (calculatingHours < 12)
            {
                calculatingMeridiem = "AM";
                // 0 am should be written as 12 am
                if (calculatingHours == 0)
                {
                    calculatingHours = 12;
                }
            }
            else
            {
                calculatingMeridiem = "PM";
                calculatingHours -= 12;
            }

            return calculatingHours.ToString() + ":" + calculatingMinutes.ToString().PadLeft(2, '0') +
                " " + calculatingMeridiem;
        }

        private long ConvertTimeToMinutes(string time)
        {
            long normalizedTime;
            string regexStringForTimeConversion = @"^(?<Hours>[\d]{1,2}):(?<minutes>\d\d)[\s]?(?<meridiem>[AP]M)$";
            Regex regexForTimeConversion = new Regex(regexStringForTimeConversion);

            Match matchedTime = regexForTimeConversion.Match(time);
            int hours, minutes;
            string meridiem;
            try
            {
                hours = Int32.Parse(matchedTime.Groups["Hours"].Value);
            }
            catch (Exception)
            {
                throw new Exception("Invalid characters in Hours!");
            }
            try
            {
                minutes = Int32.Parse(matchedTime.Groups["Minutes"].Value);
            }
            catch (Exception)
            {
                throw new Exception("Invalid characters in Minutes!");
            }
            if (meridiemValidValues.Contains( matchedTime.Groups["Meridiem"].Value))
            {
                meridiem = matchedTime.Groups["Meridiem"].Value;
            }
            else
            {
                throw new Exception("Invalid characters in Meridiem!");
            }

            // Rule: 12 PM will be 12 in a 24-hour clock, 12 AM will be 0
            if ((hours == 12) && (meridiem == "AM"))
            {
                hours = 0;
            }
            else if ((hours < 12) && (meridiem == "PM"))
            {
                hours += 12;
            }

            normalizedTime = (hours * 60) + minutes;

            return normalizedTime;

        }

    }
}