ReversePhrase.java

import java.util.List;
import java.util.ArrayList;
import java.util.*;

class Main {
  
  public static void reversePhrase(String s) {
    
    
  }
  
  public static boolean isCharOrSpace(char c){
    return isChar(c) || c == ' ';
  }
  
  public static boolean isChar(char c){
    return (c >= 'a' && c <= 'z') ||
     (c >= 'A' && c <= 'Z');
  }
  public static void main(String[] args) {

    int index = 0;
    String str = "hello world, welcome to my world";
    List<String> phrases = new ArrayList<>();
    
    while(index < str.length()){
       if(str.charAt(index)==','){
         index+=2;
       }
         String phrase = "";
         while(index < str.length()
         && isCharOrSpace(str.charAt(index))){
            phrase+=str.charAt(index);
            index++;
         }
         if(phrase.length()>0){
           phrases.add(phrase);
         } 
    }
    
    List<String> revPhrases = new ArrayList<>();
    
    for(int i=0;i<phrases.size();i++){
      String phrase = phrases.get(i);
      String reversed = "";
      boolean firstWord=true;
      index = 0;
      while(index < phrase.length()){
        char c = phrase.charAt(index);
        String word = "";
       
        while(index < phrase.length()&&isChar(phrase.charAt(index)) ){
          word+=phrase.charAt(index);
          index++;
     
        }
        
           if(word.length()>0){
          String spacedWord = word;
          
          if(firstWord){
            firstWord=false;
            
          }else{
           spacedWord+=" ";
      
          }
          reversed = spacedWord+reversed;
        }
       
        //skip space between words
        index++;      
      }
      
      if(reversed.length()>0){
          revPhrases.add(reversed);
      }
    }
   
    
    for(int i =0;i<revPhrases.size();i++)
    {
      System.out.println(revPhrases.get(i));
    }
    
  }
}