Duplicate Words

[ RegEx: ]

Duplicate Words

TASK

In this task, 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 so it will turn "I love Love to To tO code" into "I love to code" ?

To solve this task, complete the following three steps:

1. Write a RegEx that will match any repeated word.

2. Complete the second compile argument so that the compiled RegEx is case-insensitive.

3. 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.

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

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

Explanation

# RegEx

used this regular expression:

"\b(\w+)(?:\W+\1\b)+"

When using this regular expression in Java, we have to "escape" the backslash characters with additional backslashes (as done in the code above).

\w ➞ A word character: [a-zA-Z_0-9]
\W ➞ A non-word character: [^\w]
\b ➞ A word boundary
\1 ➞ Matches whatever was matched in the 1st group of parentheses,
       which in this case is the (\w+)
+ ➞ Match whatever it's placed after 1 or more times

The \b boundaries are needed for special cases such as "Bob and Andy" (we don't want to match "and" twice). Another special case is "My thesis is great" (we don't want to match "is" twice).

# Groups

input = input.replaceAll(m.group(), m.group(1))

The line of code above replaces the entire match with the first group in the match.

m.group() is the entire match

m.group(i) is the ith match. So m.group(1) is the 1st match 
           (which is enclosed in the 1st set of parentheses)

The ?: is added to make it a "non-capturing group",
       for slightly faster performance.

Hope this helps!

# Solution

DuplicateWords.java

[ External Resources: ]

Regular Expression Reference
Regex Matcher Tutorial

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HappyCoding ;) by @booleanmaybe

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