Reverse each individual word of Hello World string with Java

Question

I want to reverse each individual word of a String in Java  not the entire string  just each individual word    Example  if input String is  Hello World  then the output should be  olleH dlroW

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Know your libraries  -   import org apache commons lang StringUtils   String reverseWords String sentence        return StringUtils reverseDelimited StringUtils reverse sentence

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I know its an old post but thought to write the answer if it helps somebody  Please use the below code for proper solution   public static void main String   args           TODO Auto-generated method stub      String string1    Hello how are you        String   string2   string1 split           String result           for int i 0 i lt string2 length i                  StringBuilder stringBuilder   new StringBuilder string2 i             result    i  0   result  stringBuilder reverse   toString     result      stringBuilder reverse   toString                System out println  Result line   result       Text displayed in console  Result line olleH woh era uoy

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I came up with this answer while working on the problem  I tried not to use nested for loop solution O N 2   I kind of forced myself to use stack for fun  D      public StringBuilder reverseWord String input            char separator                char   chars   input toCharArray            Stack lt Character gt  stack   new Stack lt Character gt             StringBuilder sb   new StringBuilder chars length             for int i   0  i  lt  chars length  i                   if chars i     separator      letters                 stack push chars i                       if not last letter don t go any further                 if i    chars length - 1    continue                                while  stack isEmpty                      sb append stack pop                               sb append separator                        remove the last separator         sb deleteCharAt sb length   - 1           return sb

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if its to reverse each letter than this for loop works nicely   for int i   0  i  lt  input length    i         output   output   input substring  input length  -i -1  input length  -i

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You need to do this on each word after you split into an array of words    public String reverse String word        char   chs   word toCharArray         int i 0  j chs length-1      while  i  lt  j               swap chs i  and chs j          char t   chs i           chs i    chs j           chs j    t         i    j--            return String valueOf chs

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public static void main String   args            System out println eatWord new StringBuilder  Hello World This Is Tony s Code    new StringBuilder    new StringBuilder            static StringBuilder eatWord StringBuilder feed  StringBuilder swallowed  StringBuilder digested        for  int i   0  size   feed length    i  lt   size  i              if  feed indexOf         0    feed length      0                digested append swallowed                     swallowed   new StringBuilder              else               swallowed insert 0  feed charAt 0                      feed    feed length    gt  0     feed delete 0  1    feed             return digested      run   olleH dlroW sihT sI s ynoT edoC  BUILD SUCCESSFUL  total time  0 seconds

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Heres a method that takes a string and reverses it      public String reverse   String s                 int length   s length    last   length - 1              char   chars   s toCharArray                for   int i   0  i  lt  length 2  i                       char c   chars i                   chars i    chars last - i                   chars last - i    c                            return new String chars               First you need to split the string into words like this  String sample    hello world     String   words   sample split

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package MujeebWorkspace helps      javamujeeb gmail com   public class Mujeeb         static String str   This code is simple to reverse the word without changing positions        static String   reverse   str split             public static void main String    args              reverseMethod                 public static void reverseMethod             for  int k 0  k lt  reverse length-1  k                   String word  reverse reverse length- reverse length-k                 String subword    word                    String    splitsubword   subword split                    for  int i subword length    i gt 0  i--                    System out print splitsubword i

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This reverses the words in the given string  Words are assumed to be separated by a single space  Reversal is done in place  in the character buffer    public static String reversePhrases String s        char   buf   s toCharArray        int len   buf length      int start   0      for  int i   0  i  lt  len  i              if  buf i            i     len-1                 if  i     len-1                     i   len                            int end    start   i  2              for  int j   start  j  lt  end  j                      char c   buf j                   int pos    start   i  - j - 1                  buf j    buf pos                   buf pos    c                            start   i   1                          return new String buf

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String input    Welcome To The Java Programming           String output                String   cutAry   input split    s             StringBuilder sb   new StringBuilder            for String s cutAry               sb append s               output    sb reverse   toString                    sb replace 0  sb length                           System out println output

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String someString   new String  Love thy neighbor        System out println someString       char   someChar   someString toCharArray        int j   someChar length - 1      char temp      for  int i   0  i  lt   someChar length   2  i              temp   someChar i           someChar i    someChar j           someChar j    temp          j--            someString   new String someChar       System out println someString     Run   Love thy neighbor robhgien yht evoL

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This is my version with the same number spaces  Hope you like it guys   public String reverseWords String text           StringBuilder out   new StringBuilder            for String word   text split                    out append new StringBuilder word  reverse   toString                 out append                         return out toString   substring 0  out length   - 1

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with and without api   public class Reversal       public static void main String s             String str   hello world           reversal str              static void reversal String str           String s   str split               StringBuilder noapi new StringBuilder            StringBuilder api new StringBuilder            for String r s               noapi append reversenoapi r                api append reverseapi r                      System out println noapi toString             System out println api toString                static String reverseapi String str           StringBuilder sb new StringBuilder            sb append new StringBuilder str  reverse   toString             sb append               return sb toString                static String reversenoapi String str           StringBuilder sb new StringBuilder            for int i str length  -1 i gt  0 i--               sb append str charAt i                      sb append               return sb toString

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No one here is considering unicode characters  You need to use java text BreakIterator to find word boundaries and then use another one within each word boundary to enumerate character boundaries   String helloWorld    He u0308llo World      H  llo World StringBuilder reverseStringBuilder   new StringBuilder helloWorld length     BreakIterator wordBreakIterator   BreakIterator getWordInstance    wordBreakIterator setText helloWorld    int wordStart   wordIterator first    int wordEnd   wordIterator next     while  wordEnd    BreakIterator DONE        String word   helloWorld substring wordStart wordEnd       if  Character isLetterOrDigit word charAt 0                  Hello  or  World  in our example         BreakIterator characterBreakIterator   BreakIterator getCharacterInstance            characterBreakIterator setText word           int characterEnd   characterBreakIterator last            int characterStart   characterBreakIterator previous            while  characterStart    BreakIterator DONE                reverseStringBuilder append word substring characterStart  characterEnd                 characterEnd   characterStart              characterStart   characterBreakIterator previous                    else                  in our example         reverseStringBuilder append word             wordStart   wordEnd      wordEnd   wordIterator next       String dlroWolleh   reverseStringBuilder toString        dlroW oll  H    Using naive methods above will shift the diacritic character  u0308 above the first l when you reverse the String  You want it to stay above the e

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class ReverseWordsInString      public static String reverse String s1               int l   s1 length                if  l gt 1                      return s1 substring l-1    reverse s1 substring 0 l-1                 else                     return s1 substring 0              public static void main String   args               String st    Hello My World                String r                   for  String word   st split                           r         reverse word               System out println  Reversed words in the given string    r trim

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Solution with TC - O n  and SC - O 1   public String reverseString String str       String str    Hello Wrold       int start   0       for  int i   0  i  lt  str length    i               if  str charAt i            i    str length   - 1                 int end   0               if  i    str length   - 1                    end   i                else                   end   i - 1                             str   swap str  start  end               start   i   1                      System out println str          private static String swap String str  int start  int end         StringBuilder sb   new StringBuilder str        while  start  lt  end            sb setCharAt start  str charAt end            sb setCharAt end  str charAt start            start            end--            return sb toString

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example with stream API       public static String reverseAllWords String str        String   arr   str split           String res           for  int x   0  x  lt  arr length  x              res   res   Stream of arr x  split      reduce      a  b  - gt  b   a                   return res

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Using only substring   and recursion   public String rev String rest        if  rest equals              return         return rev rest substring 1     rest substring 0 1

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Easy way   String reverseString String string        String newString           for int x   string length   - 1  x  gt  -1  x             newString    string charAt x       return newString

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Taking into account that the separator can be more than one space tab and that we want to preserve them   public static String reverse String string        StringBuilder sb   new StringBuilder string length         StringBuilder wsb   new StringBuilder string length         for  int i   0  i  lt  string length    i                  char c   string charAt i           if  c      t     c                               if  wsb length    gt  0                                sb append wsb reverse   toString                     wsb   new StringBuilder string length   - sb length                               sb append c                     else                       wsb append c                       if  wsb length    gt  0                sb append wsb reverse   toString               return sb toString

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public String reverse String arg        char   s   arg toCharArray        StringBuilder sb   new StringBuilder        boolean reverse   false      boolean isChar   false      int insertPos   0       for  int i   0  i  lt  s length  i              isChar   Character isAlphabetic s i            if   reverse  amp  amp  isChar                sb append s i                insertPos   i              reverse   true            else if  reverse  amp  amp  isChar                sb insert insertPos  s i              else if   reverse  amp  amp   isChar                sb append s i              else if  reverse  amp  amp   isChar                reverse   false              sb append s i                         return sb toString

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This should do the trick  This will iterate through each word in the source string  reverse it using StringBuilder s built-in reverse   method  and output the reversed word   String source    Hello World    for  String part   source split             System out print new StringBuilder part  reverse   toString         System out print           Output   olleH dlroW    Notes  Commenters have correctly pointed out a few things that I thought I should mention here  This example will append an extra space to the end of the result  It also assumes your words are separated by a single space each and your sentence contains no punctuation

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Using split    you just have to change what you wish to split on   public static String reverseString String str        String   rstr      String result           int count   0      rstr   str split           String words     new String rstr length       for int i   rstr length-1  i  gt   0  i--                words count    rstr i           count               for int j   0  j  lt   words length-1  j                  result    words j                    return result

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Well I m a C C   guy  practicing java for interviews let me know if something can be changed or bettered  The following allows for multiple spaces and newlines   First one is using StringBuilder  public static String reverse String str words       StringBuilder sb result   new StringBuilder str words length         StringBuilder sb tmp   new StringBuilder        char c tmp      for int i   0  i  lt  str words length    i             c tmp   str words charAt i               if c tmp           c tmp      n                if sb tmp length      0                      sb tmp reverse                    sb result append sb tmp                   sb tmp setLength 0                                sb result append c tmp            else              sb tmp append c tmp                        if sb tmp length      0           sb tmp reverse            sb result append sb tmp             return sb result toString        This one is using char    I think its more efficient     public static String reverse String str words       char   c array   str words toCharArray        int pos start   0      int pos end      char c  c tmp       int i  j  rev length      for i   0  i  lt  c array length  i             c   c array i           if  c           c      n                if pos start    i                    pos end   i-1                  rev length    i-pos start  2                  for j   0  j  lt  rev length  j                         c tmp   c array pos start j                       c array pos start j    c array pos end-j                       c array pos end-j    c tmp                                              pos start   i 1                        redundant  if only java had   0    end of string     if pos start    i           pos end   i-1          rev length    i-pos start  2          for j   0  j  lt  rev length  j                 c tmp   c array pos start j               c array pos start j    c array pos end-j               c array pos end-j    c tmp                         return new String c array

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Reverse copy the string block-wise and then concatenate the whitespaces  for eg   hello java world    1st block    hello  reverse copy it -  olleh  and add whitespace then 2nd block    java  etc   public static void main String args          String s  rev           Scanner in   new Scanner System in        System out println  Enter a string to reverse        s   in nextLine         int length   s length           char   cs s toCharArray        int l  r      int i   0      while  i  lt  length            l   i     starting index            find length of sub-block to reverse copy         while  i  lt  length  amp  amp  s charAt i                         i                      r   i - 1     ending index         for  int j   r  j  gt   l  j--       copy reverse of sub-block             rev   rev   s charAt j                     rev   rev           add the whitespace         i               System out println  Reverse of entered string is      rev       Program also works for multiple whitespaces between words

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I m assuming you could just print the results  you just said  the output should be       -   String str    Hello World   for  String word   str split           reverse word    void reverse String s        for  int idx   s length   - 1  idx  gt   0  idx--           System out println s charAt idx        Or returning the reversed String   String str    Hello World   StringBuilder reversed   new StringBuilder    for  String word   str split           reversed append reverse word      reversed append         System out println reversed    String reverse String s      StringBuilder b   new StringBuilder      for  int idx   s length   - 1  idx  gt   0  idx--        b append s charAt idx      return b toString

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Here s the simplest solution that doesn t even use any loops   public class olleHdlroW       static String reverse String in  String out            return  in isEmpty      out                in charAt 0                        out         reverse in substring 1                     reverse in substring 1   in charAt 0    out             public static void main String args              System out println reverse  Hello World                   Even if this is homework  feel free to copy it and submit it as your own  You ll either get an extra credit  if you can explain how it works  or get caught for plagiarism  if you can t

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Use split   function and reverse individual words      public String reverseSentence String input                  String   words   input split               StringBuilder builder   new StringBuilder            for  String s   words                        String rev                    for  int i   0  i  lt  s length    i                                  rev   s charAt i    rev                             builder append rev                      return builder toString   trim              Remove the extra space that is added at the end of the new String using trim    Output       This is my sentence             sihT si ym ecnetnes

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Some of the above solutions are of the higher run time complexities  With the below algorithm  it can be achieved in O n  time   Algorithm    Parse the String from the end to beginning   Every time a space character is encountered i e       put the list of characters parsed till then in an ArrayList which can grow dynamically  Print the ArrayList in the reverse order which gives you the desired output    Complexity  O n  where n is the length of the String     import java io IOException  import java util ArrayList   public class WordReverse        public static void main String   args  throws IOException            String inputStr    Hello World           String reversed               ArrayList lt String gt  alist   new ArrayList lt String gt              for  int i   inputStr length   - 1  i  gt   0  i--                if  inputStr charAt i                            reversed   reversed   inputStr charAt i                 else                   alist add reversed                   reversed                                       alist add reversed           String result                for  int i   alist size   - 1  i  gt   0  i--                result   result   alist get i               result   result                          System out println result

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String input    Hello World         String temp           String result            for  int i   0  i  lt   input length    i              if  i    input length    amp  amp  input charAt i                        temp   input charAt i    temp            else               result   temp         result              temp                            System out println  the result is      result

[java] Reverse each individual word of "Hello World" string with Java

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