import java.util.Scanner;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class DuplicateWords {

public static void main(String[] args) {
    String regex = "\\b(\\w+)(?:\\W+\\1\\b)+";
    Pattern p = Pattern.compile(regex,Pattern.CASE_INSENSITIVE);
    Scanner in = new Scanner(System.in);
    int numSentences = Integer.parseInt(in.nextLine());

    while (numSentences-- > 0) {
        String input = in.nextLine();

        Matcher m = p.matcher(input);

        // Check for subsequences of input that match the compiled pattern
        while (m.find()) {
            input = input.replaceAll(m.group(), m.group(1));
        }

        // Prints the modified sentence.
        System.out.println(input);
    }

    in.close();
}

}

import java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern;

public class DuplicateWords {

public static void main(String[] args) {

String regex = "\\b(\\w+)(\\W+\\b\\1\\b)*";
Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);

Scanner in = new Scanner(System.in);
int numSentences = Integer.parseInt(in.nextLine());

while (numSentences-- > 0) {
    String input = in.nextLine();

    Matcher m = p.matcher(input);

    // Check for subsequences of input that match the compiled pattern
    while (m.find()) {
        input = input.replaceAll(m.group(0), m.group(1));
    }

    // Prints the modified sentence.
    System.out.println(input);
}

in.close();

} }

import java.util.Scanner; import java.util.regex.Pattern;

public class DuplicateWords {

public static void main(String[] args) {
    final String regex = "\\b(\\w+)(\\s+\\1\\b)+";
    final Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);

    final Scanner in = new Scanner(System.in);
    int numSentences = Integer.parseInt(in.nextLine());

    while (numSentences-- > 0) {
        String input = in.nextLine();
        // Replace all duplicates with first occurrence
        input = p.matcher(input).replaceAll("$1");
        System.out.println(input);
    }

This is the code I am getting the o/p same as shown but still getting the wrong answer.

    in.close();
}

}

With this code I got the same expected results except for a mysterious character at the end of the last test case. It is neither a whitespace or unprintable char. It makes no sense for me.

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class DuplicateWords {

    public static void main(String[] args) {

        String regex = "\\b(\\w+)\\s+\\1\\b";
        Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);

        Scanner in = new Scanner(System.in);
        int numSentences = Integer.parseInt(in.nextLine());
        
        while (numSentences-- > 0) {
            String input = in.nextLine();
            Matcher m = p.matcher(input);
            
            // Check for subsequences of input that match the compiled pattern
            while (m.find()) {
                input = input.replaceAll("(?i)"+regex,"$1");
                //m = p.matcher(input);
            }
            
            // Prints the modified sentence.
            System.out.print(input+'\n');
        }
			
        in.close();
    }
}

String regex = "\b(\w+)(\s+\1\b)+"; Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);

    Scanner in = new Scanner(System.in);
    int numSentences = Integer.parseInt(in.nextLine());

    while (numSentences-- > 0) {
        String input = in.nextLine();

        Matcher m = p.matcher(input);

        // Check for subsequences of input that match the compiled pattern
        while (m.find()) {
            input = input.replaceAll(m.group(), m.group(1));
        }

        // Prints the modified sentence.
        System.out.println(input);