Check if a string consists only of special characters

Given string str of length N, the task is to check if the given string contains only special characters or not. If the string contains only special characters, then print “Yes”. Otherwise, print “No”.

Examples:

Input: str = “@#$&%!~”
Output: Yes
Explanation: 
Given string contains only special characters. 
Therefore, the output is Yes.

Input: str = “Geeks4Geeks@#”
Output: No
Explanation: 
Given string contains alphabets, number, and special characters. 
Therefore, the output is No.

 

Naive Approach: Iterate over the string and check if the string contains only special characters or not. Follow the steps below to solve the problem:



  • Traverse the string and for each character, check if its ASCII value lies in the ranges [32, 47], [58, 64], [91, 96] or [123, 126]. If found to be true, it is a special character.
  • Print Yes if all characters lie in one of the aforementioned ranges. Otherwise, print No.

Time Complexity: O(N)
Auxiliary Space: O(1)

Space-Efficient Approach: The idea is to use Regular Expression to optimize the above approach. Follow the steps below:

  • Create the following regular expression to check if the given string contains only special characters or not.

    regex = “[^a-zA-Z0-9]+”

    where,

    • [^a-zA-Z0-9] represents only special characters.
    • + represents one or more times.
  • Match the given string with the Regular Expression using Pattern.matcher() in Java
  • Print Yes if the string matches with the given regular expression. Otherwise, print No.

Below is the implementation of the above approach:

Java

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// Java program to check if the string
// contains only special characters
  
import java.util.regex.*;
class GFG {
  
    // Function to check if a string
    // contains only special characters
    public static void onlySpecialCharacters(
        String str)
    {
  
        // Regex to check if a string contains
        // only special characters
        String regex = "[^a-zA-Z0-9]+";
  
        // Compile the ReGex
        Pattern p = Pattern.compile(regex);
  
        // If the string is empty
        // then print No
        if (str == null) {
            System.out.println("No");
            return;
        }
  
        // Find match between given string
        // & regular expression
        Matcher m = p.matcher(str);
  
        // Print Yes If the string matches
        // with the Regex
        if (m.matches())
            System.out.println("Yes");
        else
            System.out.println("No");
    }
  
    // Driver Code
    public static void main(String args[])
    {
        // Given string str
        String str = "@#$&%!~";
  
        // Function Call
        onlySpecialCharacters(str);
    }
}

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Output:

Yes

Time Complexity: O(N)
Auxiliary Space: O(1)

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