Check if a string is a palindrome

Question

I have a string as input and have to break the string in two substrings. If the left substring equals the right substring then do some logic.

How can I do this?

Answer 1

This is a short and efficient way of checking palindrome.

bool checkPalindrome(string inputString) {

    int length = inputString.Length;
    for(int i = 0; i < length/2; i++){
        if(inputString[i] != inputString[length-1-i]){
            return false;
        }
    }

    return true;

}

Answer 2

 public static bool IsPalindrome(string value)
        {
            int i = 0;
            int j = value.Length - 1;
            while (true)
            {
                if (i > j)
                {
                    return true;
                }
                char a = value[i];
                char b = value[j];
                if (char.ToLower(a) != char.ToLower(b))
                {
                    return false;
                }
                i++;
                j--;
            }
        }

Answer 3

public bool IsPalindroom(string input)
{
    input = input.ToLower();
    var loops = input.Length / 2;
    var higherBoundIdx = input.Length - 1;
    for (var lowerBoundIdx = 0; lowerBoundIdx < loops; lowerBoundIdx++, higherBoundIdx--)
    {
        if (input[lowerBoundIdx] != input[higherBoundIdx])
        return false;
    }
    return true;
}

Answer 4

A single line of code using Linq

public static bool IsPalindrome(string str)  
{
    return str.SequenceEqual(str.Reverse());
}

Answer 5

This C# method will check for even and odd length palindrome string (Recursive Approach):

public static bool IsPalindromeResursive(int rightIndex, int leftIndex, char[] inputString)
{
    if (rightIndex == leftIndex || rightIndex < leftIndex)
        return true;
    if (inputString[rightIndex] == inputString[leftIndex])
        return IsPalindromeResursive(--rightIndex, ++leftIndex, inputString);
    else
        return false;            
}

Answer 6

Since a palindrome also includes numbers, words, sentences, and any combinations of these, and should ignore punctuation and case, (See Wikipedia Article) I propose this solution:

public class Palindrome
{
    static IList<int> Allowed = new List<int> {
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'h',
        'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',
        'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
        '1', '2', '3', '4', '5', '6', '7', '8', '9',
        '0'
    };
    private static int[] GetJustAllowed(string text)
    {
        List<int> characters = new List<int>();
        foreach (var c in text)
             characters.Add(c | 0x20); 

        return characters.Where(c => Allowed.Contains(c)).ToArray();
    }
    public static bool IsPalindrome(string text)
    {
        if(text == null || text.Length == 1)
             return true;

        int[] chars = GetJustAllowed(text);
        var length = chars.Length;

        while (length > 0)
            if (chars[chars.Length - length] != chars[--length])
                return false;

        return true;
    }
    public static bool IsPalindrome(int number)
    {
        return IsPalindrome(number.ToString());
    }
    public static bool IsPalindrome(double number)
    {
        return IsPalindrome(number.ToString());
    }
    public static bool IsPalindrome(decimal number)
    {
        return IsPalindrome(number.ToString());
    }

}