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   Sample   public bool getStatus string myString         Example  myString    ankYkna   so if we break it into two substring it would be  left-part    ank   right-part    ank   after reversal

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public static bool IsPalindrome string value                        int i   0              int j   value Length - 1              while  true                                if  i  gt  j                                        return true                                    char a   value i                   char b   value j                   if  char ToLower a     char ToLower b                                         return false                                    i                    j--

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use this way  from dotnetperls      using System       class Program                    lt summary gt              Determines whether the string is a palindrome               lt  summary gt          public static bool IsPalindrome string value                        int min   0              int max   value Length - 1              while  true                                if  min  gt  max                                        return true                                    char a   value min                   char b   value max                       Scan forward for a while invalid                  while   char IsLetterOrDigit a                                         min                        if  min  gt  max                                                return true                                            a   value min                                         Scan backward for b while invalid                  while   char IsLetterOrDigit b                                         max--                      if  min  gt  max                                                return true                                            b   value max                                      if  char ToLower a     char ToLower b                                         return false                                    min                    max--                                   static void Main                         string   array                                  A man  a plan  a canal  Panama                     A Toyota  Race fast  safe car  A Toyota                     Cigar  Toss it in a can  It is so tragic                     Dammit  I m mad                     Delia saw I was ailed                     Desserts  I stressed                     Draw  O coward                     Lepers repel                     Live not on evil                     Lonely Tylenol                     Murder for a jar of red rum                     Never odd or even                     No lemon  no melon                     Senile felines                     So many dynamos                     Step on no pets                     Was it a car or a cat I saw                      Dot Net Perls is not a palindrome                     Why are you reading this                     This article is not useful                                               Test                              foreach  string value in array                                Console WriteLine   0     1    value  IsPalindrome value

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class Program       static void Main string   args                 string s  revs               Console WriteLine   Enter string            s   Console ReadLine            for  int i   s Length - 1  i  gt   0  i--    String Reverse                       Console WriteLine i               revs    s i  ToString                      if  revs    s     Checking whether string is palindrome or not                       Console WriteLine  String is Palindrome                      else                       Console WriteLine  String is not Palindrome                      Console ReadKey

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If you just need to detect a palindrome  you can do it with a regex  as explained here  Probably not the most efficient approach  though

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Here is an absolutely simple way to do this     Receive the word as input into a method  Assign a temp variable to the original value  Loop through the initial word  and add the last character to the reversal that you are constructing until the inital word has no more characters  Now use the spare you created to hold the original value to compare to the constructed copy    This is a nice way as u don t have to cast ints and doubles  U can just pass them to the method in their string representation by using the ToString   method   public static bool IsPalindrome string word                string spare   word          string reversal   null          while  word Length  gt  0                        reversal   string Concat reversal  word LastOrDefault                 word   word Remove word Length - 1                     return spare Equals reversal           So from your main method   For even and odd length strings u just pass the whole string into the method

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public bool Solution string content                int length   content Length           int half   length 2           int isOddLength   length 2              Counter for checking the string from the middle          int j    isOddLength  0    half half 1           for int i half-1 i gt  0 i--                                        if content i     content j                                return false                            j                       return true

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This c  method will check for even and odd lengh palindrome string  public static bool IsPalenDrome string palendromeString                        bool isPalenDrome   false               try                               int halfLength   palendromeString Length   2                   string leftHalfString   palendromeString Substring 0 halfLength                    char   reversedArray   palendromeString ToCharArray                    Array Reverse reversedArray                   string reversedString   new string reversedArray                    string rightHalfStringReversed   reversedString Substring 0  halfLength                    isPalenDrome   leftHalfString    rightHalfStringReversed   true   false                            catch  Exception ex                                throw ex                             return isPalenDrome

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static void Main string   args                        Console WriteLine  Enter a string to check pallingdrome i e startreverse is same                string str   Convert ToString  Console ReadLine                  char   arr   str ToCharArray                var strLength   arr Length-1              string newStr                   for  var i  strLength  i  lt  arr Length  i--                                 newStr   newStr   Convert ToString arr i                    if i  0                                        break                                              if str  newStr                                Console WriteLine  Entered key is Palindrome                    Console ReadLine                              else                               Console WriteLine  Entered key is not Palindrome                    Console ReadLine

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Out of all the solutions  below can also be tried   public static bool IsPalindrome string s        return s    new string s Reverse   ToArray

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int length   myString Length  for  int i   0  i  lt  length   2  i          if  myString i     myString length - i - 1           return false    return true

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private void CheckIfPalindrome string str                           place string in array of chars             char   array   str ToCharArray                 int length   array Length -1               Boolean palindrome  true              for  int i   0  i  lt   length  i     go through the array                               if  array i     array length    compare if the char in the same positions are the same eg  tattarrattat  will compare array 0  t with array 11   t if are not the same stop the for loop                                       MessageBox Show  not                        palindrome   false                      break                                     else   if they are the same make length smaller by one and do the same                                                         length--                                               if  palindrome  MessageBox Show  Palindrome

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This way is both concise in appearance  amp  processes very quickly   Func lt string  bool gt  IsPalindrome   s   gt  s Reverse   Equals s

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Shortest technique to find Palindrome using conventional way   public string IsPalindrome string Word        int i   0  j   Word Length - 1      for    i  lt  Word Length - 1  amp  amp  j  gt   0  amp  amp  Word i     Word j   i    j--        return j    0    Palindrome     Not Palindrome

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A single line of code using Linq  public static bool IsPalindrome string str          return str SequenceEqual str Reverse

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using System  using System Collections Generic  using System Linq  using System Text  using System Threading Tasks    class palindrome       static void Main string   args                Console Write  Enter a number             string panstring   Console ReadLine            Palindrome panstring           Console ReadKey               static int index   0       public static void Palindrome string strexcluding                try                       string reversecounter   string Empty               for  int i   strexcluding Length - 1  i  gt   0  i--                                if  strexcluding i  ToString      null                      reversecounter    strexcluding i  ToString                              if  reversecounter    strexcluding                                Console WriteLine  Palindrome Number      strexcluding                             else                               Sum strexcluding                                    catch Exception ex                        Console WriteLine ex ToString                          public static void Sum string stringnumber                try                       index                string number1   stringnumber              string number2   stringnumber              string   array   new string number1 Length               string obtained   string Empty              string sreverse   null               Console WriteLine index     step       number1         number2                for  int i   0  i  lt  number1 Length  i                                  int temp1   Convert ToInt32 number1 number1 Length - i - 1  ToString                     int temp2   Convert ToInt32 number2 number2 Length - i - 1  ToString                      if  temp1   temp2  gt   10                                        if  number1 Length - 1    number1 Length - 1 - i                                                array i      temp1   temp2  - 10  ToString                            obtained    one                                             else if  number1 Length - 1    i                                                if  obtained     one                                                         array i     temp1   temp2   1  ToString                                                      else                                                       array i     temp1   temp2  ToString                                                                        else                                               if  obtained     one                                                         array i      temp1   temp2   1  - 10  ToString                                                      else                                                       array i      temp1   temp2  - 10  ToString                                obtained    one                                                                                       else                                       if  obtained     one                           array i     temp1   temp2   1  ToString                        else                         array i     temp1   temp2  ToString                        obtained    Zero                                                 for  int i   array Length - 1  i  gt   0  i--                                if  array i     null                      sreverse    array i  ToString                               Palindrome sreverse                     catch Exception ex                        Console WriteLine ex ToString

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Using LINQ and off course far from the best solution  var original    ankYkna   var reversed   new string original Reverse   ToArray     var palindrom   original    reversed

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public Boolean IsPalindrome string value       var one   value ToList lt char gt        var two   one Reverse lt char gt    ToList       return one Equals two

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String extension method  easy to use       public static bool IsPalindrome this string str                str   new Regex    a-zA-Z    Replace str      ToLower            return  str Where  t  i    gt  t    str str Length - i - 1   Any

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public  bool MojTestPalindrome  string word                bool yes   false           char  test1   word ToArray            char   test2   test1 Reverse   ToArray            for  int i 0  i lt  test2 Length  i                           if  test1 i     test2 test2 Length - 1 - i                                  yes   false                  break                             else                      yes   true                                    if  yes    true                        return true                    else              return false

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public static bool getStatus string myString        string first   myString Substring 0  myString Length   2       char   arr     myString ToCharArray         Array Reverse arr        string temp     new string arr       string second   temp Substring 0  temp Length   2        return first Equals second

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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 lt int gt  Allowed   new List lt int gt             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 lt int gt  characters   new List lt int gt             foreach  var c in text               characters Add c   0x20             return characters Where c   gt  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  gt  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

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The various provided answers are wrong for numerous reasons  primarily from misunderstanding what a palindrome is  The majority only properly identify a subset of palindromes   From Merriam-Webster     A word  verse  or sentence  such as  Able was I ere I saw Elba     And from Wordnik     A word  phrase  verse  or sentence that reads the same backward or forward  For example  A man  a plan  a canal  Panama    Consider non-trivial palindromes such as  Malayalam   it s a proper language  so naming rules apply  and it should be capitalized   or palindromic sentences such as  Was it a car or a cat I saw   or  No  X  in Nixon    These are recognized palindromes in any literature   I m lifting the thorough solution from a library providing this kind of stuff that I m the primary author of  so the solution works for both String and ReadOnlySpan lt Char gt  because that s a requirement I ve imposed on the library  The solution for purely String will be easy to determine from this  however   public static Boolean IsPalindrome this String  string    gt         string is null   amp  amp   string AsSpan   IsPalindrome     public static Boolean IsPalindrome this ReadOnlySpan lt Char gt  span           First we need to build the string without any punctuation or whitespace or any other        unrelated-to-reading characters      StringBuilder builder   new StringBuilder span Length       foreach  Char s in span            if    s IsControl                  s IsPunctuation                  s IsSeparator                  s IsWhiteSpace                      builder Append s                       String prepped   builder ToString        String reversed   prepped Reverse   Join           Now actually check it s a palindrome     return String Equals prepped  reversed  StringComparison CurrentCultureIgnoreCase       You re going to want variants of this that accept a CultureInfo parameter as well  when you re testing a specific language rather than your own language  by instead calling  ToUpper cultureInfo  on prepped   And here s proof from the projects unit tests that it works

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Just for fun   return myString SequenceEqual myString Reverse

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public static  bool IsPalindrome string word                          first reverse the string             string reversedString   new string word Reverse   ToArray                 return string Compare word  reversedString     0   true   false

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public static bool IsPalindrome string str                int i   0          int a   0           char   chr   str ToCharArray            foreach  char cr in chr                        Array Reverse chr               if  chr i     cr                                if  a    str Length                                        return true                                    a                    i                              else                               return false                                  return true

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public static bool palindrome string t                int i   t Length          for  int j   0  j  lt  i   2  j                          if  t j     t i - j-1                                 continue                            else                               return false                  break                                  return true

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string test    Malayalam               char   palindrome   test ToCharArray                char   reversestring   new char palindrome Count                 for  int i   palindrome Count   - 1  i  gt   0  i--                                reversestring palindrome Count   - 1 - i    palindrome i                               string materializedString   new string reversestring                if  materializedString ToLower      test ToLower                                  Console Write  Palindrome                               else                               Console Write  Not a Palindrome                                Console Read

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In C     public bool EhPalindromo string text     var reverseText   string Join     text ToLower   Reverse      return reverseText    text

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That is non-trivial  there is no built in method to do that for you  you ll have to write your own  You will need to consider what rules you would like to check  like you implicitly stated you accepted reversing of one string  Also  you missed out the middle character  is this only if odd length    So you will have something like   if myString length   2   0           even      string a   myString substring 0  myString length   2        string b   myString substring myString length   2   1  myString lenght 2         if a    b             return true          Rule 1  reverse      if a    b reverse      can t remember if this is a method  if not you ll have to write that too            return true    etc  also doing whatever you want for odd strings

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static void Main string   args        string str  rev          Console Write  Enter string         str   Console ReadLine         for  int i   str Length - 1  i  gt   0  i--                rev   rev   str i              if  rev    str          Console Write  Entered string is pallindrome        else         Console Write  Entered string is not pallindrome         Console ReadKey

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This is a short and efficient way of checking palindrome   bool checkPalindrome string inputString         int length   inputString Length      for int i   0  i  lt  length 2  i             if inputString i     inputString length-1-i                return false                       return true

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protected bool CheckIfPalindrome string text        if  text    null                string strToUpper   Text ToUpper            char   toReverse   strToUpper ToCharArray            Array Reverse toReverse            String strReverse   new String toReverse           if  strToUpper    toReverse                        return true                    else                       return false                      else               return false            Use this the sipmlest way

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public bool IsPalindroom string input        input   input ToLower        var loops   input Length   2      var higherBoundIdx   input Length - 1      for  var lowerBoundIdx   0  lowerBoundIdx  lt  loops  lowerBoundIdx    higherBoundIdx--                if  input lowerBoundIdx     input higherBoundIdx           return false            return true

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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  lt  leftIndex          return true      if  inputString rightIndex     inputString leftIndex           return IsPalindromeResursive --rightIndex    leftIndex  inputString       else         return false

[c#] Check if a string is a palindrome

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