function to remove duplicate characters in a string

Question

The following code is trying to remove any duplicate characters in a string  I m not sure if the code is right  Can anybody help me work with the code  i e whats actually happening when there is a match in characters    public static void removeDuplicates char   str      if  str    null  return    int len   str length    if  len  lt  2  return    int tail   1    for  int i   1  i  lt  len    i        int j      for  j   0  j  lt  tail    j          if  str i     str j   break            if  j    tail          str tail    str i           tail              str tail    0

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Well I came up with the following solution. Keeping in mind that S and s are not duplicates. Also I have just one hard coded value.. But the code works absolutely fine.

public static String removeDuplicate(String str) {

    StringBuffer rev = new StringBuffer();  
    rev.append(str.charAt(0));

    for(int i=0; i< str.length(); i++)
    {
        int flag = 0;
        for(int j=0; j < rev.length(); j++)
        {
            if(str.charAt(i) == rev.charAt(j))
            {
                flag = 0;
                break;
            }
            else
            {
                flag = 1;
            }
        }
        if(flag == 1)
        {
            rev.append(str.charAt(i));
        }
    }

    return rev.toString();
}

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public class RemoveRepeatedCharacters                   This method removes duplicates in a given string in one single pass         Keeping two indexes  go through all the elements and as long as subsequent characters match  keep        moving the indexes in opposite directions  When subsequent characters don t match  copy value at higher index        to  lower   1  index         Time Complexity   O n         Space    O 1                      public static void removeDuplicateChars String text             char   ch   text toCharArray            int i   0    first index         for int j   1  j  lt  ch length  j                  while i  gt   0  amp  amp  j  lt  ch length  amp  amp  ch i     ch j                     i--                  j                    System out println  i       i     j       j                                              if j  lt  ch length                    ch   i    ch j                                       Print the final string         for int k   0  k  lt   i  k                System out print ch k                public static void main String   args             String text    abccbdeefgg           removeDuplicateChars text

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Java  Avoiding usage of Map  List data structures   private String getUniqueStr String someStr        StringBuilder uniqueStr   new StringBuilder                if someStr    null           for int i 0  i  lt someStr length    i                if uniqueStr indexOf String valueOf someStr charAt i       -1                 uniqueStr append someStr charAt i                                         return uniqueStr toString

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package com java exercise   public class RemoveCharacter                    param args             public static void main String   args            RemoveCharacter rem   new RemoveCharacter            char   ch rem GetDuplicates  JavavNNNNNNC  toCharArray             char   desiredString  JavavNNNNNNC  toCharArray            System out println rem RemoveDuplicates desiredString  ch               char   GetDuplicates char   input                int ctr 0          char   charDupl new char 20           for  int i   0  i  lt input length  i                          char tem input i               for  int j  0  j  lt  i  j                                  if  tem    input j                                         charDupl ctr      input j                                                        return charDupl             public char   RemoveDuplicates char   input1  char   input2                   int coutn  0           char   out2   new char 10            boolean flag   false           for  int i   0  i  lt  input1 length  i                            for  int j   0  j  lt  input2 length  j                                         if  input1 i     input2 j                                                   flag   false                           break                                              else                                                 flag   true                                                      if  flag                                  out2 coutn    input1 i                    flag   false                                     return out2

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char   chars   s toCharArray        HashSet lt Character gt  charz   new HashSet lt Character gt          for Character c   s toCharArray                   if  charz contains c                         charz add c                 System out print c                        for Character c   charz                System out print c

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This would be much easier if you just looped through the array and added all new characters to a list  then retruned that list   With this approach  you need to reshuffle the array as you step through it and eventually redimension it to the appropriate size in the end

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Yet another solution  seems to be the most concise so far   private static String removeDuplicates String s                   String x   new String s            for int i 0 i lt x length  -1 i                x   x substring 0 i 1     x substring i 1   replace String valueOf x charAt i                  return x

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An improved version for using bitmask to handle 256 chars   public static void removeDuplicates3 char   str       long map     new long    0  0  0  0     long one   1     for  int i   0  i  lt  str length  i             long chBit    one  lt  lt   str i  64        int n    int  str i  64       if   map n   amp  chBit    gt  0     duplicate detected         str i    0      else    add unique char as a bit  1  to the map         map n     chBit             get rid of those   0 s   int wi   1    for  int i 1  i lt str length  i            if  str i   0  str wi      str i             setting the rest as   0    for   wi lt str length  wi    str wi    0      Result     1  ASDJasanwAaw            --0        1 ASDJasnw      -0   double quotes not included

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I understand that this is a Java question  but since I have a nice solution which could inspire someone to convert this into Java  by all means  Also I like answers where multiple language submissions are available to common problems   So here is a Python solution which is O n  and also supports the whole ASCII range  Of course it does not treat  a  and  A  as the same   I am using 8 x 32 bits as the hashmap   Also input is a string array using dedup list  some string     def dedup str       map    0 0 0 0 0 0 0 0      for i in range len str            ascii   ord str i           slot   ascii   32         bit   ascii   32         bitOn   map slot   amp   1  lt  lt  bit          if bitOn              str i               else              map slot     1  lt  lt  bit      return    join str    also a more pythonian way to do this is by using a set   def dedup s       return    join list set s

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private static String removeDuplicateCharactersFromWord String word         String result   new String           for  int i   0  i  lt  word length    i              if   result contains      word charAt i                  result         word charAt i                        return result

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program to remove the duplicate character in string       Author senthilkumar M    char  dup remove char  str         int i   0  j   0  l   strlen str       int flag   0  result   0       for i   0  i  lt  l  i               result   str i  -  a            if flag  amp   1  lt  lt  result                     if duplicate found remove  amp  shift the array                for j   i  j  lt  l  j                        str j    str j 1                               i--                l--     duplicates removed so string length reduced by 1 character                continue                      flag     1  lt  lt  result               return str

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This will solve purpose in fast and simple code  It gives result in O n    void removeduplicate char  str        int checker   0      int cnt   0      for int i   0  i  lt  strlen str   i                  int val     str   i  -  int  a           if   checker  amp   1  lt  lt  val    gt  0  continue          else                 str   cnt      str   i               cnt                      checker     1  lt  lt  val               str cnt      0

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public class RemoveDuplicateInString       public static void main String   args            String s    ABCDDCA           RemoveDuplicateInString rs   new RemoveDuplicateInString            System out println rs removeDuplicate s                public String removeDuplicate String s            String retn   null          boolean   b   new boolean 256            char   ch   s toCharArray            for  int i   0  i  lt  ch length  i                   if  b ch i                      ch i                                   else                   b ch i     true                                    retn   new String ch           return retn

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public class StringRedundantChars                   param args             public static void main String   args               initializing the string to be sorted         String sent    I love painting and badminton              Translating the sentence into an array of characters         char   chars   sent toCharArray             System out println  Before Sorting            showLetters chars              Sorting the characters based on the ASCI character code           java util Arrays sort chars            System out println  Post Sorting            showLetters chars            System out println  Removing Duplicates            stripDuplicateLetters chars            System out println  Post Removing Duplicates              Sorting to collect all unique characters          java util Arrays sort chars           showLetters chars                          This function prints all valid characters in a given array  except empty values                 param chars Input set of characters to be displayed             private static void showLetters char   chars             int i   0            The following loop is to ignore all white spaces         while    0     chars i                 i                      for    i  lt  chars length  i                  System out print       chars i                      System out println               private static char   stripDuplicateLetters char   chars                Basic cursor that is used to traverse through the unique-characters         int cursor   0             Probe which is used to traverse the string for redundant characters         int probe   1           for    cursor  lt  chars length - 1                     Checking if the cursor and probe indices contain the same                characters             if  chars cursor     chars probe                     System out println  Removing char       chars probe                       Please feel free to replace the redundant character with                    character  I have used   0                  chars probe      0                      Pushing the probe to the next character                 probe                  else                      Since the probe has traversed the chars from cursor it means                    that there were no unique characters till probe                     Hence set cursor to the probe value                 cursor   probe                     Push the probe to refer to the next character                 probe                                    System out println             return chars

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public String removeDuplicateChar String nonUniqueString        String uniqueString           for  char currentChar   nonUniqueString toCharArray              if   uniqueString contains      currentChar                 uniqueString    currentChar                       return uniqueString

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public static void main String   args         char   str      a    b    a   b   c   e   c          for  int i   1  i  lt  str length  i              for  int j   0  j  lt  i  j                  if  str i     str j                     str i                                            System out println str

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Using guava you can just do something like Sets newHashSet charArray  toArray    If you are not using any libraries  you can still use new HashSet lt Char gt    and add your char array there

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Substringing method  Concatenation is done with  concat   to avoid allocation additional memory for left hand and right hand of    Note  This removes even duplicate spaces   private static String withoutDuplicatesSubstringing String s            for int i   0  i  lt  s length    i               String sub   s substring i 1             int index   -1            while  index   sub toLowerCase   indexOf Character toLowerCase s charAt i      gt  -1  amp  amp   sub isEmpty                   sub   sub substring 0  index  concat sub substring index 1  sub length                            s   s substring 0  i 1  concat sub                     return s          Test case   String testCase1    nanananaa  baaaaatmaan  batman     Output  na  btm

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The function looks fine to me  I ve written inline comments  Hope it helps      function takes a char array as input     modifies it to remove duplicates and adds a 0 to mark the end    of the unique chars in the array  public static void removeDuplicates char   str      if  str    null  return     if the array does not exist  nothing to do return    int len   str length     get the array length    if  len  lt  2  return     if its less than 2  can t have duplicates  return    int tail   1     number of unique char in the array       start at 2nd char and go till the end of the array    for  int i   1  i  lt  len    i         int j         for every char in outer loop check if that char is already seen         char in  0 tail  are all unique      for  j   0  j  lt  tail    j          if  str i     str j   break     break if we find duplicate               if j reachs tail  we did not break  which implies this char at pos i        is not a duplicate  So we need to add it our  unique char list         we add it to the end  that is at pos tail      if  j    tail          str tail    str i      add         tail     increment tail    0 tail  is still  unique char list              str tail    0     add a 0 at the end to mark the end of the unique char

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I couldn t understand the logic behind the solution so I wrote my simple solution     public static void removeDuplicates char   str         if  str    null  return    If the string is null return           int length   str length    Getting the length of the string     if  length  lt  2  return    Return if the length is 1 or smaller      for int i 0  i lt length  i       Loop through letters on the array          int j           for j i 1 j lt length j       Loop through letters after the checked letters  i                if  str j   str i      If you find duplicates set it to 0                  str j  0

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Given the following question       Write code to remove the duplicate characters in a string without   using any additional buffer  NOTE  One or two additional variables   are fine  An extra copy of the array is not    Since one or two additional variables are fine but no buffer is allowed  you can simulate the behaviour of a hashmap by using an integer to store bits instead  This simple solution runs at O n   which is faster than yours  Also  it isn t conceptually complicated and in-place        public static void removeDuplicates char   str            int map   0          for  int i   0  i  lt  str length  i                  if   map  amp   1  lt  lt   str i  -  a      gt  0     duplicate detected                 str i    0              else    add unique char as a bit  1  to the map                 map    1  lt  lt   str i  -  a                      The drawback is that the duplicates  which are replaced with 0 s  will not be placed at the end of the str   array  However  this can easily be fixed by looping through the array one last time  Also  an integer has the capacity for only regular letters

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String s    Javajk       List lt Character gt  charz   new ArrayList lt Character gt         for  Character c   s toCharArray              if    charz contains Character toUpperCase c      charz                  contains Character toLowerCase c                   charz add c                        ListIterator litr   charz listIterator       while  litr hasNext              Object element   litr next           System err println       element                this will remove the duplicate if the character present in both the case

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This is my solution  public static String removeDup String inputString       if  inputString length   lt 2  return inputString      if  inputString  null  return null      char   inputBuffer inputString toCharArray        for  int i 0 i lt inputBuffer length i             for  int j i 1 j lt inputBuffer length j                 if  inputBuffer i   inputBuffer j                    inputBuffer j  0                                    String result new String inputBuffer       return result

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Question  Remove Duplicate characters in a string Method 1   Python   import collections  a    GiniGinaProtijayi   aa   collections OrderedDict   fromkeys a  print    join aa     Method 2   Python   a    GiniGinaProtijayi  list      aa     list append ch  for ch in a if  ch  not in list  print     join list     IN Java   class test2      public static void main String   args      String a    GiniGinaProtijayi    List lt Character gt  list   new ArrayList lt  gt             for int i   0   i  lt  a length    i                 char ch   a charAt i              if  list size      0    list add ch               if  list contains ch    list add ch                for        StringBuffer sbr   new StringBuffer           for  char ch   list   sbr append ch          System out println sbr           main     end

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This function removes duplicate from string inline  I have used C  as a coding language and the duplicates are removed inline           public static void removeDuplicate char   inpStr                        if  inpStr    null  return              if  inpStr Length  lt  2  return           for  int i   0  i  lt  inpStr Length    i                         int j  k              for  j   1  j  lt  inpStr Length  j                                   if  inpStr i     inpStr j   amp  amp  i    j                                        for  k   j  k  lt  inpStr Length - 1  k                                                  inpStr k    inpStr k   1                                             inpStr k                                                              Console WriteLine inpStr

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I resolve a similar exercise of the book   crackring the coding interview using recursion   package crackingcodeinterview   public class Exercise    static String textString    this is a random text of example        452464156    public static void main String   args         filterLetters 0          public static void filterLetters int position  String letters        if  position    textString length               boolean p   false           for  int i   0  i  lt  letters length    i                  if  letters charAt i     textString charAt position                     p   true                  break                                   if   p                letters    textString charAt position                     position            filterLetters position  letters         else           System out println letters                 Other solution using substring and recursion  public class MyClass   public static void main String args           getUnicLetter  esta es una cadena con letras repetidas               public static String getUnicLetter String originalWord String finalWord           if originalWord isEmpty    return  null          System out print finalWord           return getUnicLetter originalWord replace originalWord substring 0 1      finalWord contains originalWord substring 0 1          originalWord substring 0 1

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A O n  solution   import java util    import java io     public class String Duplicate Removal    public static String duplicate removal String s                if s length   lt 2              return s           else if s length    2                        if s charAt 0   s charAt 1                   s   Character toString s charAt 0                return s                     boolean    arr   new boolean 26            for int i 0 i lt s length   i                           if arr s charAt i - a    false                  arr s charAt i - a   true               else                               s    new StringBuilder s   deleteCharAt i   toString                    i--                                  return s                public static void main String    args                String s    abbashbhqa           System out println duplicate removal s

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I have written a piece of code to solve the problem  I have checked with certain values  got the required output   Note  It s time consuming    static void removeDuplicate String s         char s1     s toCharArray         Arrays sort s1                        Sorting is performed  a to z                   Since adjacent values are compared      int myLength   s1 length              Length of the character array is stored here      int i   0                             i refers to the position of original char array     int j   0             j refers to the position of char array after skipping the duplicate values       while i    myLength-1             if s1 i   s1 i 1          Compares two adjacent characters  if they are not the same             s1 j    s1 i          if not same  then  first adjacent character is stored in s j              s1 j 1    s1 i 1      Second adjacent character is stored in s j 1              j                     j is incremented to move to next location                    i                         i is incremented              the length of s is i  i gt j      String s4   new String  s1            Char Array to String        s4 0  to s4 j 1  contains the length characters after removing the duplicate       s4 j 2  to s4 i  contains the last set of characters of the original char array      System out println s4 substring 0  j 1         Feel free to run my code with your inputs  Thanks

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This is my solution  The algorithm is mainly the same as the one in the book  quot Cracking the code interview quot  where this exercise comes from  but I tried to improve it a bit and make the code more understandable  public static void removeDuplicates char   str               if string has less than 2 characters  it can t contain            duplicate values  so there s nothing to do         if  str    null    str length  lt  2                return                        variable which indicates the end of the part of the string             which is  cleaned   all duplicates removed          int tail   0           for  int i   0  i  lt  str length  i                  boolean found   false                              check if character is already present in                the part of the array before the current char             for  int j   0  j  lt  i  j                      if  str j     str i                         found   true                      break                                                  if char is already present                skip this one and do not copy it             if  found                    continue                                copy the current char to the index                 after the last known unique char in the array             str tail    str i               tail                                                 str tail      0          One of the important requirements from the book is to do it in-place  as in my solution   which means that no additional data structure should be used as a helper while processing the string  This improves performance by not wasting memory unnecessarily

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include  lt iostream gt   include  lt string gt  using namespace std   int main            your code goes here     string str      cin  gt  gt  str      long map   0      for int  i  0  i  lt  str length     i             if  map  amp   1L  lt  lt  str i     gt  0               str i    0                    else              map    1L  lt  lt  str i                       cout  lt  lt  str      return 0

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public static void main  String    args                String s    aabbbeeddsfre    sample string         String temp2      string with no duplicates         HashMap lt Integer Character gt  tc   new HashMap lt Integer Character gt      create a hashmap to store the char s         char    charArray   s toCharArray            for  Character c   charArray   for each char                       if   tc containsValue c    if the char is not already in the hashmap                                       temp2 temp2 c toString     add the char to the output string                     tc put c hashCode   c    and add the char to the hashmap                                      System out println temp2    final string         instead of HashMap I think we can use Set too

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Your code is  I m sorry to say  very C-like   A Java String is not a char    You say you want to remove duplicates from a String  but you take a char   instead   Is this char    0-terminated  Doesn t look like it because you take the whole  length of the array  But then your algorithm tries to  0-terminate a portion of the array  What happens if the arrays contains no duplicates   Well  as it is written  your code actually throws an ArrayIndexOutOfBoundsException on the last line  There is no room for the  0 because all slots are used up   You can add a check not to add  0 in this exceptional case  but then how are you planning to use this code anyway  Are you planning to have a strlen-like function to find the first  0 in the array  And what happens if there isn t any   due to all-unique exceptional case above     What happens if the original String char   contains a  0   which is perfectly legal in Java  by the way  see JLS 10 9 An Array of Characters is Not a String   The result will be a mess  and all because you want to do everything C-like  and in place without any additional buffer  Are you sure you really need to do this  Why not work with String  indexOf  lastIndexOf  replace  and all the higher-level API of String  Is it provably too slow  or do you only suspect that it is    Premature optimization is the root of all evils   I m sorry but if you can t even understand what the original code does  then figuring out how it will fit in the bigger  and messier  system will be a nightmare     My minimal suggestion is to do the following    Make the function takes and returns a String  i e  public static String removeDuplicates String in  Internally  works with char   str   in toCharArray    Replace the last line by return new String str  0  tail     This does use additional buffers  but at least the interface to the rest of the system is much cleaner     Alternatively  you can use StringBuilder as such   static String removeDuplicates String s        StringBuilder noDupes   new StringBuilder        for  int i   0  i  lt  s length    i              String si   s substring i  i   1           if  noDupes indexOf si     -1                noDupes append si                       return noDupes toString        Note that this is essentially the same algorithm as what you had  but much cleaner and without as many little corner cases  etc

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public class RemoveCharsFromString    static String testcase1    No  I am going to Noida   static String testcase2    goings    public static void main String args   throws StringIndexOutOfBoundsException      RemoveCharsFromString testInstance  new RemoveCharsFromString        String result   testInstance remove testcase1 testcase2       System out println result        write your code here public String remove String str  String str1 throws StringIndexOutOfBoundsException         String result null           if  str    null          return           try            for  int i   0  i  lt  str1 length     i                     char ch1 str1 charAt i           for int j 0 j lt str length   j                          char ch   str charAt  j            if  ch    ch1                    String s4 String valueOf ch           String s5  str replaceAll s4               str s5                                         catch Exception e                   result str      return result

[java] function to remove duplicate characters in a string

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