Reverse String with Special Characters in Java

If you're given a string that has both an alphabet (from "a" to "z" as well as "A" to "Z") as well as a special character, you need to reverse the string without changing the special character.

Example:

Input: s = "j,s$v"

Output: s = "v,s$j"

Take note that neither $ nor, are relocated.

The only reversed subsequence is "jsv."

Input: str = "Bc,d,ef!$"

Output: str = "fe,d,cB!$"

Easy Resolution:

Make a character array with the name temp[ ].
Copy alphabetical characters to temp[ ] from the provided array.
Apply the common string reversal method to temp[ ].
Now perform a single loop iteration over the input string as well as the temporary data. Replace any alphabetic characters in the input string with the current temp[ ]character.

The application of the above strategy is seen below:

File name: ReverseStringSpcl.java

// Reversing a string without impacting 
// the special characters is demonstrated using Java code.
import java.util.*;
 
class ReverseStringSpcl {
    public static void rev(char str[], int l1, int r1)
    {
        for (int i1 = l1; i1 < r1 / 2; i1++) {
            char t = str[i1];
            str[i1] = str[r1 - 1 - i1];
            str[r1 - 1 - i1] = t;
        }
    }
    public static void reverse(char str[])
    {
        // creating a character array of the size
        // equal to the length of the string
        char[] t = new char[str.length];
        int x1 = 0;
        for (int i1 = 0; i1 < str.length; i1++) {
            if (str[i1] >= 'a' && str[i1] <= 'z'
                || str[i1] >= 'A' && str[i1] <= 'Z') {
                // storing the elements in the array
                t[x1] = str[i1];
                x1++;
            }
        }
 
        // reverse the character array
        rev(t, 0, x1);
 
        x1 = 0;
        for (int i1 = 0; i1 < str.length; i1++) {
            if (str[i1] >= 'a' && str[i1] <= 'z'
                || str[i1] >= 'A' && str[i1] <= 'Z') {
                // update the original string
                str[i1] = t[x1];
                x1++;
            }
        }
 
        String rS = new String(str);
        System.out.println(" The string after reversing is: " + rS);
    }
 
    // Main Code
    public static void main(String args[])
    {
        String s = "aB,C,De!$";
        char[] cA = s.toCharArray();
        reverse(cA);
    }
} 

Output:

The string after reversing is: eD,C,Ba!$

Time Complexity: O(N), where N is the string's length.

Space Complexity: O(N), where N represents the string's length.

Effective Approach

The above solution has an O(n) time complexity, but it uses more space and traverses the input string twice.

With just one traversal and no additional room, we can reverse. The algorithm is listed below.

1) Let the input string be "s[]" and the string length be "n1".
2) l1 = 0, r1 = n1-1
3) While l1 is smaller than r1, do following
    a) If s[l1] is not an alphabetic character, do l1++
    b) Else If s[r1] is not an alphabetic character, do r1--
    c) Else swap s[l1] and s[r1]

The aforementioned method is implemented in the ways listed below.

File name: ReverseStringSpcl1.java

// To demonstrate how and where to 
// reverse a word without damaging the
// special characters, below is some Java code.
import java.io.*;
class ReverseStringSpcl1 {
    public static void reverse(char s[])
    {
        // Initializing the l1 and r1 pointers
        int r1 = s.length - 1, l1 = 0;
 
        // Traversing the string from both ends until 'l1' and 'r1'
        while (l1 < r1) {
            // Ignoring the special characters
            if (!Character.isAlphabetic(s[l1]))
                l1++;
            else if (!Character.isAlphabetic(s[r1]))
                r1--;
 
            // Both s[l1] and s[r1] are not special characters
            else {
                char t = s[l1];
                s[l1] = s[r1];
                s[r1] = t;
                l1++;
                r1--;
            }
        }
    }
    // Driver Code
    public static void main(String args[])
    {
        String s = "b!!!c.d.e,f'g,hij";
        char[] cA = s.toCharArray();
 
        System.out.println(" Given string is: " + s);
        reverse(cA);
        String rS = new String(cA);
 
        System.out.println(" The string after revrsing is: " + rS);
    }
}

Output:

Given string is: b!!!c.d.e,f'g,hij
 The string after reversing is: j!!!i.h.g,f'e,dcb

Time Complexity: O(N), where N is the string's length.

Space Complexity: O (1).

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