How to move chars in char array to the left and to the right in c# sharp

Question

guys! I have this situation: Given a string and two more characters X and Y. Move all X characters to the beginning of the string and all Y characters to the end of the string. The order of the other characters in the string remains unchanged. I wrote two function MoveCharsLeft and MoveCharsRight to move X to the left and Y to the right, but there is an error System.IndexOutOfRangeException: 'Index was outside the bounds of the array.' on this line of code char toReplace = splitText[charToCheck]; and I don't know how to handle it, in order to solve the exercise. Can, you guys, help me with that, how should be the functions?

static void Main()
    {
        string text = Console.ReadLine();
        char[] splitText = text.ToCharArray();
        string firstLetter = Console.ReadLine();
        char[] firstChar = firstLetter.ToCharArray();
        string secondLetter = Console.ReadLine();
        char[] secondChar = secondLetter.ToCharArray();
        char one = firstChar[0];
        char two = secondChar[0];
        Console.WriteLine(CheckChars(splitText, one, two));
        Console.ReadLine();
    }

    static char[] CheckChars(char[] splitText, char one, char two)
    {
        for (char letter = 'a'; letter <= 'z'; letter++)
        {
            if (Array.IndexOf(splitText, one) > -1)
            {
                MoveCharsLeft(splitText, one);
            }

            if (Array.IndexOf(splitText, two) > -1)
            {
                MoveCharsRight(splitText, two);
            }
        }

        return splitText;
    }

    static void MoveCharsLeft(char[] splitText, char charToCheck)
    {
        char toReplace = splitText[charToCheck];
        char currentLetter = splitText[0];
        for (int i = 0; i <= charToCheck; i++)
        {
            char temporary = splitText[i];
            splitText[i] = currentLetter;
            currentLetter = temporary;
        }

        splitText[0] = toReplace;
    }

    static void MoveCharsRight(char[] splitText, char charToCheck)
    {
        char toReplace = splitText[charToCheck];
        char currentLetter = splitText[-1];
        for (int i = 0; i <= charToCheck; i++)
        {
            char temporary = splitText[i];
            splitText[i] = currentLetter;
            currentLetter = temporary;
        }

        splitText[-1] = toReplace;
    }

Shadowchaser · Accepted Answer · 2020-10-14T13:59:37.657

You're not checking your boundaries. I would say CheckChars method is redundant and in MoveCharsLeft and MoveCharsRight you're not checking if you're still inside of splitText.

Here's how I would implement MoveCharsLeft, I hope it'll guide you in the right direction.

char[] MoveCharactersLeft(char[] text, char character) {
    var lowerCharacter = char.ToLower(character);
    var left = new List<char>();
    var right = new List<char>();
    
    foreach (var letter in text) {
        if (char.ToLower(letter) == lowerCharacter) {
            left.Add(letter);
            continue;
        }
        
        right.Add(letter);
    }
    
    left.AddRange(right);
    return left.ToArray();
}

And here's MoveCharactersRight:

char[] MoveCharactersRight(char[] text, char character) {
    var lowerCharacter = char.ToLower(character);
    var left = new List<char>();
    var right = new List<char>();
    
    foreach (var letter in text) {
        if (char.ToLower(letter) == lowerCharacter) {
            right.Add(letter);
            continue;
        }
        
        left.Add(letter);
    }
    
    left.AddRange(right);
    return left.ToArray();
}

Now that you have both you simply call MoveCharsLeft and then the MoveCharactersRight on the result of MoveCharsLeft.

thank you for your solution, it works for first user's character, but I think you missed the part in which we have the second character ( the Y) from the user and it should be moved in the right: Move all X characters to the beginning of the string and all Y characters to the end of the string. Can u help me with that too? I saw in c# negative index doesn't exist. — , Oct 14 '20 at 13:52
You just need to modify two lines to get it, but OK, I've added it now. — Shadowchaser, Oct 14 '20 at 14:00

score 0 · Answer 2 · answered Oct 14 '20 at 14:01

You can swap them in place, although it requires a lot of copying. Here's a function to move a character from one spot to another in an array. You can find several examples of this on the web and SO.

    public static void Move(char[] buffer, int from, int too)
    {
        if (from == too)
            return;

        char temp = buffer[from];

        if (too < from)
        {
            Array.Copy(buffer, too, buffer, too + 1, from - too);
        }
        else
        {
            Array.Copy(buffer, from + 1, buffer, from, too - from);
        }

        buffer[too] = temp;
    }

Then you just have to iterate through the array testing the characters, testing them and moving them to the right spot. Here's a function to do that:

    public static void ArrangeChars(char[] buffer, char left, char right)
    {
        int leftIndex = 0;
        int rightIndex = buffer.Length - 1;

        int i = 0;

        while(i <= rightIndex)
        {
            char ch = buffer[i];

            if (ch == left && i > leftIndex)
                Move(buffer, i, leftIndex++);
            else if (ch == right && i < rightIndex)
                Move(buffer, i, rightIndex--);
            else
                ++i;
        }
    }

Call it like so:

    static void Main(string[] _)
    {
        char[] data = "test me and move".ToCharArray();

        Console.WriteLine(new string(data));

        ArrangeChars(data, 'e', 't');

        Console.WriteLine("Move 'e' to start, move 't' to end");

        Console.WriteLine(new string(data));
    }

The usual caveats apply - this has not been well tested and if you use it, you should check all the edge cases.

How to move chars in char array to the left and to the right in c# sharp

2 Answers2