I want to reverse a string. input: Computer; This input contains 4 whitespaces in the beginning of the word 'computer'.I want to include these 4 whitespaces in the beginning of the reversed string also.So,the program should include all the whitespaces I put at the beginning while taking the reverse too(I put 4 whitespaces as an example only). output:" retupmoc"; I am attaching my code here.

package BasicTesting;
import java.util.*;

    public class Corrected_StringRev {
    
        public static void main(String[] args) {
            Scanner sc= new Scanner(System.in); //System.in is a standard input stream  
            System.out.print("Enter a string: ");  
            String str= sc.nextLine();        
            String reversed = reverseString( str );
            
            System.out.println( reversed );
        }
        
        public static String reverseString( String newString ) {
            
            char ch[]=newString.toCharArray();  
            String rev="";  
            for(int i=ch.length-1;i>=0;i--){  
                rev =ch[i];  
            }  
            return rev;  
       
        }
    }

How can I change this code to include the above requirement.Please,rewrite the code.Hope ypu will help.Thanks in adavance!

CodePudding user response：

The logic is simple:

1. Traverse the start of the string and add whitespaces to rev until you meet the first non-whitespace
2. Do your string reversal and stop before the whitespace section begins

public static String reverseString(String newString) {
    char ch[] = newString.toCharArray();  
    String rev = "";
    int nWhitespace;
    for (nWhitespace = 0; nWhitespace < ch.length; nWhitespace  ) {
        if (!Character.isWhitespace(ch[i]) {
            break;
        }
        rev  = ch[i];
    }

    for(int i = ch.length - 1; i >= nWhitespace; i--){  
        rev  = ch[i];  
    }
    return rev;  
}

By the way, you can improve your code by using StringBuilder instead of =.

CodePudding user response：

Here instead of keeping a count and then adding it, we will be checking if the character we are at currently in the string is a whitespace character. If yes, we add a space to our string builder.

As soon as we come across a non-whitespace character, we break out of the loop.

strB.append(new StringBuilder(inputString.trim()).reverse().toString());
        return strB.toString();

What this code does is:

• Take string inputString and trim it (remove trailing and leading whitespaces.
• Creates a new (anonymous) object of a StringBuilder and reverses it. Convert it into a string to append it to our original StringBuilder strB after the whitespaces. Finally, we convert it into String and return it.

Some tips:

• I will be using StringBuilder as it is mutable so saves space and also it contains a function to reverse it directly.
• You should not call the length function of string in the loop as it will call it for every loop. Better to store the value in a variable and use that variable in the loop.

public static String reverseString(String inputString) {
        StringBuilder strB = new StringBuilder();
        int len = inputString.length();
        for(int i=0;i<len;i  ){
            if(inputString.charAt(i) == ' '){
                strB.append(" ");
            }
            else
                break;
        }
        strB.append(new StringBuilder(inputString.trim()).reverse().toString());
        return strB.toString();
    }