JavaRegexDuplicateWords.java

// Problem: 
//
// In this challenge, we use regular expressions (RegEx) to remove instances of words that are repeated more than once, 
// but retain the first occurrence of any case-insensitive repeated word. 
// For example, the words love and to are repeated in the sentence I love Love to To tO code. 
// Can you complete the code in the editor so it will turn I love Love to To tO code into I love to code?
//
// To solve this challenge, complete the following three lines:
//
// Write a RegEx that will match any repeated word.
// Complete the second compile argument so that the compiled RegEx is case-insensitive.
// Write the two necessary arguments for replaceAll such that each repeated word 
// is replaced with the very first instance the word found in the sentence. 
// It must be the exact first occurrence of the word, as the expected output is case-sensitive.
//            
//
// Note: This challenge uses a custom checker; you will fail the challenge 
// if you modify anything other than the three locations that the comments direct you to complete. 
// To restore the editor's original stub code, create a new buffer 
// by clicking on the branch icon in the top left of the editor.
//
// Input Format
//
// The following input is handled for you the given stub code:
//
// The first line contains an integer, n, denoting the number of sentences.
// Each of the n subsequent lines contains a single sentence consisting of 
// English alphabetic letters and whitespace characters.
//
// Constraints
//
// Each sentence consists of at most 10^4 English alphabetic letters and whitespaces.
// 1<=n<=100
//
// Output Format
//
// Stub code in the editor prints the sentence modified by the replaceAll line to stdout. 
// The modified string must be a modified version of the initial sentence where all repeat occurrences of each word are removed.
//
// Sample Input
// 5
// Goodbye bye bye world world world
// Sam went went to to to his business
// Reya is is the the best player in eye eye game
// in inthe
// Hello hello Ab aB
//
// Sample Output
// Goodbye bye world
// Sam went to his business
// Reya is the best player in eye game
// in inthe
// Hello Ab
//
// Explanation
// 1. We remove the second occurrence of bye and the second and third occurrences of "world" from "Goodbye bye bye world world world" to get "Goodbye bye world".
// 2. We remove the second occurrence of "went" and the second and third occurrences of "to" from "Sam went went to to to his business" to get "Sam went to his business".
// 3. We remove the second occurrence of "is", the second occurrence of "the", and the second occurrence of "eye" from 
//    "Reya is is the the best player in eye eye game" to get "Reya is the best player in eye game".
// 4. The sentence "in inthe" has no repeated words, so we do not modify it.
// 5. We remove the second occurrence of "ab" from "Hello hello Ab aB" to get "Hello Ab". 
//    It's important to note that our matching is case-insensitive, and we specifically retained the first occurrence of the matched word in our final string.
//



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([a-z]+)\\b(?:\\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);
        }

        in.close();
    }
}