Java: Check a string follows a specified pattern

Last update on May 13 2025 13:00:19 (UTC/GMT +8 hours)

String Follows Pattern

Write a Java program to check if a string follows a given pattern.

Example pattern:
Given pattern = "xyyx", str = "red black black red", return true.
Given pattern = "xyyx", str = "red black black green", return false.
Given pattern = "xxxx", str = "red black black red", return false.
Given pattern = "xxxx", str = "red red red red", return true.

Visual Presentation:

Sample Solution:

Java Code:

// Import Scanner and Map classes from java.util package for user input and data storage
import java.util.*;

// Main class for the solution
public class Solution {
    // Main method to execute the solution
    public static void main(String[] args) {
        // Sample input strings for testing word pattern matching
        String str = "red black black red";
        // String str = "red red red red"; 
        String pattern = "xyxx";
        // String pattern = "xxxx";
        
        // Display the result of the word_Pattern_Match function
        System.out.print("Is the string and pattern matched? " + word_Pattern_Match(pattern, str));
    }

    // Function to check if a given string follows a given word pattern
    public static boolean word_Pattern_Match(String pattern, String str) {
        // Convert the pattern string to an array of characters
        char[] word_pattern = pattern.toCharArray();
        
        // Split the input string into an array of words using space as a delimiter
        String[] words = str.split(" ");

        // Create a HashMap to store the mapping between characters and words
        Map map = new HashMap<>();
        
        // Create a HashSet to check for duplicate mappings
        Set set = new HashSet<>();

        // Iterate through the characters in the pattern
        for (int i = 0; i < word_pattern.length; i++) {
            // Check if the character is already mapped
            if (map.containsKey(word_pattern[i])) {
                // Check if the mapped word is different from the current word in the array
                if (!map.get(word_pattern[i]).equals(words[i])) {
                    return false;
                }
                continue;
            }

            // Check if the current word is already mapped to another character
            if (set.contains(words[i])) {
                return false;
            }
            
            // Add the mapping between the character and the current word to the HashMap
            map.put(word_pattern[i], words[i]);
            
            // Add the current word to the HashSet to mark it as used
            set.add(words[i]);
        }

        // If all conditions are satisfied, return true
        return true;
    }
} 

Sample Output:

Is the string and pattern matched? false

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to check if a string matches a pattern that includes wildcard characters like '*' and '?'.
• Write a Java program to convert a simple pattern into a regular expression and validate a string against it.
• Write a Java program to verify if a string conforms to a pattern that includes repeated groups of characters.
• Write a Java program to perform a case-insensitive pattern matching check on a given string.

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