Removing duplicates from a String in Java

Question

I am trying to iterate through a string in order to remove the duplicates characters   For example the String aabbccdef should become abcdef and the String abcdabcd should become abcd  Here is what I have so far   public class test        public static void main String   args             String input   new String  abbc            String output   new String             for  int i   0  i  lt  input length    i                  for  int j   0  j  lt  output length    j                      if  input charAt i     output charAt j                         output   output   input charAt i                                                      System out println output               What is the best way to do this

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package com st removeduplicate   public class RemoveDuplicate      public static void main String   args        String str1  shushil  str2               for int i 0  i lt  str1 length  -1 i              int count 0          for int j 0 j lt  i j                  if str1 charAt i   str1 charAt j                    count                if count  gt 1                  break                    if count  1               str2 str2 str1 charAt i             System out println str2

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String str    eamparuthik gmail com       char   c   str toCharArray        String op            for int i 0  i lt  c length-1  i             if  op contains c i                 op   op   c i             System out println op

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String input    abbcccaabbddeessacccbbddefgaabbccddeeffggadscsda       String output           for  int i  0  i lt input length   i              if   output contains input substring i  i 1                 output   output  input substring i  i 1                    System out println output

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Here is an improvement to the answer by Dave   It uses HashSet instead of the slightly more costly LinkedHashSet  and reuses the chars buffer for the result  eliminating the need for a StringBuilder   String string    aabbccdefatafaz    char   chars   string toCharArray    Set lt Character gt  present   new HashSet lt  gt     int len   0  for  char c   chars      if  present add c           chars len      c   System out println new String chars  0  len         abcdeftz

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For the simplicity of the code- I have taken hardcore input  one can take input by using Scanner class also      public class KillDuplicateCharInString       public static void main String args              String str   aaaabccdde            char arr    str toCharArray            int n   arr length          String finalStr             for int i 0 i lt n i                  if i  n-1                   finalStr  arr i                   break                            if arr i   arr i 1                     continue                            else                   finalStr  arr i                                   System out println finalStr

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public class RemoveRepeated4rmString        public static void main String   args            String s    harikrishna           String s2               for  int i   0  i  lt  s length    i                  Boolean found   false              for  int j   0  j  lt  s2 length    j                      if  s charAt i     s2 charAt j                         found   true                      break    don t need to iterate further                                             if  found    false                    s2   s2 concat String valueOf s charAt i                                     System out println s2

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Convert the string to an array of char  and store it in a LinkedHashSet   That will preserve your ordering  and remove duplicates   Something like   String string    aabbccdefatafaz    char   chars   string toCharArray    Set lt Character gt  charSet   new LinkedHashSet lt Character gt     for  char c   chars        charSet add c      StringBuilder sb   new StringBuilder    for  Character character   charSet        sb append character     System out println sb toString

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import java util LinkedHashMap  import java util Map Entry   public class Sol        public static void main String   args            char   str    bananas  toCharArray            LinkedHashMap lt Character Integer gt  map   new LinkedHashMap lt  gt             StringBuffer s   new StringBuffer             for Character c   str               if map containsKey c                   map put c  map get c  1               else                 map put c  1                      for Entry lt Character Integer gt  entry   map entrySet                 s append entry getKey                        System out println s

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Try this simple solution using Set collection concept  String str    aabbcdegg        Set lt Character gt removeduplicates   new LinkedHashSet lt  gt         char strarray    str toCharArray        for char c strarray                removeduplicates add c               Iterator lt Character gt  itr   removeduplicates iterator        while itr hasNext                  System out print itr next

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public String removeDuplicates String dupCharsString       StringBuffer buffer   new StringBuffer dupCharsString       int step   0      while step  lt   buffer length             for  int i   step   1  i  lt  buffer length    i                  if  buffer charAt i     buffer charAt step                     buffer setCharAt i                                        step              return buffer toString   replaceAll    s

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public static void main  String   args         Scanner sc   new Scanner System in       String s   sc next        String str           char c      for int i   0  i  lt  s length    i                  c   s charAt i           str   str   c          s   s replace c                if i    s length   - 1                       System out println str replaceAll    s

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I would use the help of LinkedHashSet  Removes dups  as we are using a Set  maintains the order as we are using linked list impl   This is kind of a dirty solution  there might be even a better way   String s  aabbccdef   Set lt Character gt  set new LinkedHashSet lt Character gt     for char c s toCharArray          set add Character valueOf c

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Create a StringWriter  Run through the original string using charAt i  in a for loop  Maintain a variable of char type keeping the last charAt value  If you iterate and the charAt value equals what is stored in that variable  don t add to the StringWriter  Finally  use the StringWriter toString   method and get a string  and do what you need with it

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Here is another logic I d like to share  You start comparing from midway of the string length and go backward   Test with  input    azxxzy   output    ay    String removeMidway String input           cnt   cnt 1          StringBuilder str   new StringBuilder input           int midlen   str length   2          for int i midlen-1 i gt 0 i--                for int j midlen j lt str length  -1 j                          if str charAt i   str charAt j                        str delete i  j 1                       midlen   str length   2                      System out println  i   i   j   j    len    str length       midlen     midlen     after deleted       str                                                            return str toString

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String input    AAAB        String output           for  int index   0  index  lt  input length    index              if  input charAt index   input length       input                  charAt  index   1    input length                    output    input charAt index                        System out println output     but you cant use it if the input has the same elements  or if its empty

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import java io BufferedReader  import java io IOException  import java io InputStreamReader   public class RemoveDuplicacy           public static void main String args   throws IOException                       BufferedReader br   new BufferedReader new InputStreamReader System in                System out print  Enter any word                   String s   br readLine                int l   s length                char ch              String ans                   for int i 0  i lt l  i                                  ch   s charAt i                   if ch                           ans   ans   ch                  s   s replace ch         Replacing all occurrence of the current character by a space                           System out println  Word after removing duplicate characters       ans

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Java 8 has a new String chars   method which returns a stream of characters in the String  You can use stream operations to filter out the duplicate characters like so   String out   in chars                mapToObj c - gt  Character valueOf  char  c      bit messy as chars   returns an IntStream  not a CharStream  which doesn t exist               distinct                map Object  toString               collect Collectors joining

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package StringPrograms   public class RemoveDuplicateCharacters        public static void main String   args               TODO Auto-generated method stub         boolean flag          String str    quot Stackoverflowtest quot           String a    quot  quot           int dlen   a length            for  int i   0  i  lt  str length    i                  flag   false              for  int j   0  j  lt dlen  j                                      if  str charAt i     a charAt j                         flag   true                      break                                if  flag    false                    a   a   str charAt i                   dlen   dlen   1                                  System out println a

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public static String removeDuplicateChar String str            char charArray     str toCharArray             StringBuilder stringBuilder  new StringBuilder             for int i 0 i lt charArray length i                  int index   stringBuilder toString   indexOf charArray i                 if index  lt   -1                    stringBuilder append charArray i                                       return stringBuilder toString

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public static void main String   args         int i j      StringBuffer str new StringBuffer        Scanner in   new Scanner System in       System out print  Enter string           str append in nextLine          for  i 0 i lt str length  -1 i                  for  j 1 j lt str length   j                          if  str charAt i   str charAt j                   str deleteCharAt j                       System out println  Removed String      str

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Code to remove the duplicate characters in a string without using any additional buffer  NOTE  One or two additional variables are fine  An extra array is not   import java util    public class Main      public static char   removeDupes char   arr           if  arr    null    arr length  lt  2              return arr          int len   arr length          int tail   1          for int x   1  x  lt  len  x                 int y              for y   0  y  lt  tail  y                     if  arr x     arr y   break                            if  y    tail                   arr tail    arr x                   tail                                    return Arrays copyOfRange arr  0  tail              public static char   bigArr int len           char   arr   new char len           Random r   new Random            String alphabet    abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890       amp    -              lt  gt                 for int x   0  x  lt  len  x                 arr x    alphabet charAt r nextInt alphabet length                         return arr            public static void main String args              String result   new String removeDupes new char    a    b    c    d    a              assert  abcd  equals result     abcda should return abcd but it returns      result           result   new String removeDupes new char    a    a    a    a              assert  a  equals result     aaaa should return a but it returns      result           result   new String removeDupes new char    a    b    c    a              assert  abc  equals result     abca should return abc but it returns      result           result   new String removeDupes new char    a    a    b    b              assert  ab  equals result     aabb should return ab but it returns      result           result   new String removeDupes new char    a              assert  a  equals result     a should return a but it returns      result           result   new String removeDupes new char    a    b    b    a              assert  ab  equals result     abba should return ab but it returns      result            char   arr   bigArr 5000000           long startTime   System nanoTime            System out println  2      new String removeDupes arr             long endTime   System nanoTime            long duration    endTime - startTime           System out println  Program took      duration     nanoseconds            System out println  Program took      duration 1000000000     seconds               How to read and talk about the above code    The method called removeDupes takes an array of primitive char called arr  arr is returned as an array of primitive characters  by value    The arr passed in is garbage collected at the end of Main s member method removeDupes  The runtime complexity of this algorithm is O n  or more specifically O n  small constant   the constant being the unique characters in the entire array of primitive chars   The copyOfRange does not increase runtime complexity significantly since it only copies a small constant number of items   The char array called arr is not stepped all the way through  If you pass null into removeDupes  the method returns null  If you pass an empty array of primitive chars or an array containing one value  that unmodified array is returned  Method removeDupes goes about as fast as physically possible  fully utilizing the L1 and L2 cache  so Branch redirects are kept to a minimum    A 2015 standard issue unburdened computer should be able to complete this method with an primitive char array containing 500 million characters between 15 and 25 seconds    Explain how this code works   The first part of the array passed in is used as the repository for the unique characters that are ultimately returned   At the beginning of the function the answer is   the characters between 0 and 1  as between 0 and tail     We define the variable y outside of the loop because we want to find the first location where the array index that we are looking at has been duplicated in our repository   When a duplicate is found  it breaks out and quits  the y  tail returns false and the repository is not contributed to   when the index x that we are peeking at is not represented in our repository  then we pull that one and add it to the end of our repository at index tail and increment tail     At the end  we return the array between the points 0 and tail  which should be smaller or equal to in length to the original array   Talking points exercise for coder interviews   Will the program behave differently if you change the y   to   y   Why or why not   Does the array copy at the end represent another  N  pass through the entire array making runtime complexity O n n  instead of O n     Why or why not   Can you replace the double equals comparing primitive characters with a  equals   Why or why not   Can this method be changed in order to do the replacements  by reference  instead of as it is now   by value    Why or why not   Can you increase the efficiency of this algorithm by sorting the repository of unique values at the beginning of  arr    Under which circumstances would it be more efficient

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public static void main String a           String name  Madan         System out println name         StringBuilder sb new StringBuilder name         for int i 0 i lt name length   i               for int j i 1 j lt name length   j                  if name charAt i   name charAt j                  sb deleteCharAt j                                            System out println  After deletion    sb

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StringBuilder builderWord   new StringBuilder word    for int index 0  index  lt  builderWord length    index         for int reverseIndex builderWord length  -1  reverseIndex  gt  index reverseIndex--         if  builderWord charAt reverseIndex     builderWord charAt index            builderWord deleteCharAt reverseIndex                 return builderWord toString

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import java util Scanner   public class dublicate       public static void main String    a            System out print  Enter the String            Scanner Sc   new Scanner System in           String st Sc nextLine            StringBuilder sb new StringBuilder            boolean    bc new boolean 256           for int i 0 i lt st length   i                          int index st charAt i               if bc index   false                                sb append st charAt i                    bc index  true                                   System out print sb toString

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Another possible solution  in case a string is an ASCII string  is to maintain an array of 256 boolean elements to denote ASCII character appearance in a string  If a character appeared for the first time  we keep it and append to the result  Otherwise just skip it   public String removeDuplicates String input        boolean   chars   new boolean 256       StringBuilder resultStringBuilder   new StringBuilder        for  Character c   input toCharArray              if   chars c                 resultStringBuilder append c               chars c    true                      return resultStringBuilder toString        This approach will also work with Unicode string  You just need to increase chars size

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Okay Guys  I have found a better way to do this  public static void alpha char   finalname        if  finalname    null                return             if  finalname length  lt 2                return             char empty     000       for  int i 0  i lt finalname length-1  i                  if  finalname i     finalname i 1                         finalname i    empty                       String alphaname   String valueOf finalname       alphaname   alphaname replace   000            System out println alphaname

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Using Stream makes it easy   noDuplicates   Arrays asList myString split                            stream                         distinct                         collect Collectors joining          Here is some more documentation about Stream and all you can do with   it     https   docs oracle com javase 8 docs api java util stream package-summary html      The  description  part is very instructive about the benefits of Streams

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public class RemoveDuplicatesFromStingsMethod1UsingLoops        public static void main String   args             String input   new String  aaabbbcccddd            String output               for  int i   0  i  lt  input length    i                  if   output contains String valueOf input charAt i                       output    String valueOf input charAt i                                    System out println output             output  abcd

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Try this simple solution   public String removeDuplicates String input       String result           for  int i   0  i  lt  input length    i              if  result contains String valueOf input charAt i                   result    String valueOf input charAt i                        return result

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You can t  You can create a new String that has duplicates removed  Why aren t you using StringBuilder  or StringBuffer  presumably    You can run through the string and store the unique characters in a char   array  keeping track of how many unique characters you ve seen  Then you can create a new String using the String char    int  int  constructor   Also  the problem is a little ambiguous mdash does  ldquo duplicates rdquo  mean adjacent repetitions   In other words  what should happen with abcab

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Simple solution is to iterate through the given string and put each unique character into another string in this case  a variable result   if this string doesn t contain that particular character Finally return result string as output   Below is working and tested code snippet for removing duplicate characters from the given string which has O n  time complexity    private static String removeDuplicate String s          String result           for  int i 0  i lt s length   i                char ch   s charAt i             if   result contains    ch                   result     ch                            return result        If the input is madam then output will be mad  If the input is anagram then output will be angrm  Hope this helps  Thanks

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ve an array to know whether a character has already been recorded or not  if not  add that to the string buffer  Please note that I have made it case sensitive  with the int array  you can always make it  ve not done that in this code  to return the number of occurrences too   private static String removeDuplicates String s         int    occurrences   new int 52       Arrays fill occurrences 0        StringBuffer deDupS   new StringBuffer        for int i   0  i  lt  s length    i              if s charAt i   gt   97                if occurrences s charAt i  - 97     0                    deDupS append s charAt i                    occurrences s charAt i  - 97                             else if s charAt i   gt   65                if occurrences s charAt i  - 65   26     0                    deDupS append s charAt i                    occurrences s charAt i  - 65   26                                        return deDupS toString

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public class StringTest        public static String dupRemove String str             Set lt Character gt  s1   new HashSet lt Character gt             StringBuffer sb   new StringBuffer            for  int i   0  i  lt  str length    i                   Character c   str charAt i                if   s1 contains c                     s1 add c                   sb append c                                      System out println sb toString              return sb toString                public static void main String   args             dupRemove  AAAAAAAAAAAAAAAAA BBBBBBBB

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Hope this will help   public void RemoveDuplicates         String s    Hello World        int l   s length        char ch      String result           for  int i   0  i  lt  l  i              ch   s charAt i           if  ch                       result   result   ch                       Replacing space in all occurrence of the current character         s   s replace ch                  System out println  After removing duplicate characters       result

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Oldschool way  as we wrote such a tasks in Apple    Basic  adapted to Java    int i j  StringBuffer str new StringBuffer    Scanner in   new Scanner System in   System out print  Enter string      str append in nextLine      for  i 0 i lt str length  -1 i         for  j i 1 j lt str length   j             if  str charAt i   str charAt j               str deleteCharAt j           System out println  Removed non-unique symbols      str

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I think working this way would be more easy     Just pass a string to this function and the job is done       private static void removeduplicate String name      char   arr   name toCharArray        StringBuffer modified  new StringBuffer        for char a arr                if  modified contains Character toString a                          modified modified append Character toString a                         System out println modified

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This is another approach   void remove duplicate  char  str  int len        unsigned int index   0      int c   0      int i   0      while  c  lt  len               this is just example more check can be added for            capital letter  space and special chars             int pos   str c  -  a           if   index  amp   1 lt  lt pos      0                str i      str c               index     1 lt  lt pos                     c              str i    0

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This is improvement on solution suggested by  Dave  Here  I am implementing in single loop only       Let s reuse the return of set add T item  method and add it simultaneously in StringBuffer if add is successfull   This is just O n   No need to make a loop again   String string    aabbccdefatafaz    char   chars   string toCharArray    StringBuilder sb   new StringBuilder    Set lt Character gt  charSet   new LinkedHashSet lt Character gt     for  char c   chars        if charSet add c             sb append c            System out println sb toString        abcdeftz

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package com core interview client   import java util LinkedHashSet   import java util Scanner   import java util Set   public class RemoveDuplicateFromString    public static String DupRemoveFromString String str           char   c1  str toCharArray         Set lt Character gt  charSet   new LinkedHashSet lt Character gt           for char c c1            charSet add c               StringBuffer sb   new StringBuffer            for  Character c2   charSet                sb append c2                 return sb toString        public static void main String   args          System out println  Enter Your String            Scanner sc   new Scanner System in         String str   sc nextLine          System out println DupRemoveFromString str

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Solution using JDK7   public static String removeDuplicateChars final String str        if  str    null    str isEmpty             return str             final char   chArray   str toCharArray        final Set lt Character gt  set   new LinkedHashSet lt  gt         for  char c   chArray            set add c              final StringBuilder sb   new StringBuilder        for  Character character   set            sb append character             return sb toString

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val str  karunkumardev    val arr str toCharArray     val len arr size-1    for i in 0  len         var flag false       for j in i 1  len             if arr i   arr j                 flag true               break                           if  flag             print arr i

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String output    quot  quot       HashMap lt Character Boolean gt  map   new HashMap lt  gt         for int i 0 i lt str length   i             char ch   str charAt i           if   map containsKey ch                output    ch              map put ch true                       return output   This is the simple approach using HashMap in Java in one pass   Time Complexity   O n  Space Complexity   O n

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String str1     Hi helloo helloo  oooo this  split         Set lt String gt  charSet   new LinkedHashSet lt String gt     for  String c  str1            charSet add c      StringBuilder sb   new StringBuilder     for  String character   charSet            sb append character       System out println sb toString

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To me it looks like everyone is trying way too hard to accomplish this task  All we are concerned about is that it copies 1 copy of each letter if it repeats  Then because we are only concerned if those characters repeat one after the other the nested loops become arbitrary as you can just simply compare position n to position n   1  Then because this only copies things down when they re different  to solve for the last character you can either append white space to the end of the original string  or just get it to copy the last character of the string to your result    String removeDuplicate String s        String result            for  int i   0  i  lt  s length    i             if  i   1  lt  s length    amp  amp  s charAt i     s charAt i 1                result   result   s charAt i                     if  i   1    s length                 result   result   s charAt i                        return result

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Arrays stream input split      distinct   collect joining

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String s    WelcomeToJava   String result       List lt String gt  al   new ArrayList lt String gt      for  int i   0  i  lt  s length    i          for  int k   0  k  lt  s length    k              if  String valueOf s charAt i   equalsIgnoreCase String valueOf s charAt k                   if   al contains String valueOf s charAt i                       al add String valueOf s charAt i                     result   result   String valueOf s charAt i                                     System out println  Result--    result

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public class RemoveDuplicate        static String st  papuuu       static String st1         public static void main String   args            for  int i   0  i  lt  st length    i                  String ff   String valueOf st charAt i                if   st1 contains ff                     st1   st1   st charAt i                                      System out println st1

[java] Removing duplicates from a String in Java

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