How I get the output like output string?

Question

I am trying to solve this issue in so many times. But I can't understand how to get numeric value respected ASCII character.

By following this steps:

1. Replace the character in even position with their corresponding ASCII value
2. Reverse the string using StringBuilder.

Input string:--->

?85O89*69R65*87O104*33I104

Output should be like this:--->

?uoy*era*woH*!iH

How I get the output In java?

Answer 1

Unlike the others I think this is actually an interesting question, that a newbie may find difficult to understand.

Given the string

?85O89*69R65*87O104*33I104

We see there is repetitive pattern, a character + a numeric value. We have then

?85
O89
*69
R65
*87
O104
*33
I104  

Based on the proposed output we understand the number represents an ASCII codepoint .
Also we see that the case of each character is reversed.

Thus, we may write the following code.

final String value = "?85O89*69R65*87O104*33I104";
final StringBuilder sb = new StringBuilder();

// We split the string based on the \w(\d+) pattern, "reversed"
final String[] parts = value.split("(?=([^\\d]+))");

for (final String s : parts) {
   // For each character we must reverse its case
   // The first symbol is already in a presentable form
   final char c = s.charAt(0);
   sb.append(Character.isUpperCase(c) ? Character.toLowerCase(c) : Character.toUpperCase(c));

   // The remaining part represents an ASCII symbol in decimal form
   final int codePoint = Integer.parseInt(s.substring(1));
   final String str = new String(Character.toChars(codePoint));
   sb.append(Character.isUpperCase(codePoint) ? str.toLowerCase() : str.toUpperCase());
}

System.out.println(sb);

Which will correctly print

?uoy*era*woH*!iH

Answer 2

The input string seems to be using * as "word" delimiters which should be kept in the output.

A "word" contains 3 characters, the first and the last characters are displayed as ASCII codes in the encoded string.

When decoding a word, the case of the letter character has to be inverted: lower -> upper, upper -> lower.

That being said, the following implementation may be as follows:

static Pattern WORD = Pattern.compile("(\\d+)(.)(\\d+)");

public static String decode(String str) {
    return Arrays
        .stream(str.split("((?<=[*!\\?])|(?=[*!\\?]))"))
        .map(s -> s.matches(WORD.pattern()) ? decodeWord(s) : s)
        .collect(Collectors.joining());
}

private static String decodeWord(String word) {
    Matcher match = WORD.matcher(word);
    if (match.find()) {
        return new StringBuilder()
            .append(decodeChar((char)(Integer.parseInt(match.group(1)))))
            .append(decodeChar(match.group(2).charAt(0)))
            .append(decodeChar((char)(Integer.parseInt(match.group(3)))))
            .toString();
    }
    return ""; 
}

static char decodeChar(char c) {
    if (Character.isLetter(c)) {
        return Character.isUpperCase(c) ? Character.toLowerCase(c) : Character.toUpperCase(c);
    }
    return c;
}

Test:

System.out.println(decode("?85O89*69R65*87O104*33I104"));

Output:

?uoy*era*woH*!iH

Answer 3

According to what you said, and base on the string you give, I'm ASSUMING that every even position is between(not include the ending) two non-numbers.

    public static String perform(String str) {
        StringBuilder sb = new StringBuilder("");
        
        String dump = "";//dump string
        for(int i = 0;i<str.length();i++) {//Read the string char by char
            int ascii = (int) str.charAt(i);//work with ASCII
            
            if(ascii - '0' < 0 || ascii - '0' > 9) {//check if ascii is a non-number
                
                if(dump.length() != 0) {//can dump
                    int c = Integer.parseInt(dump);
                    
                    if(c >= 65 && c <= 90) {//uppercase to lowercase
                        sb.append((char) (c - 'A' + 'a'));
                    }
                    
                    if(c >= 97 && c <= 122) {//lowercase to uppercase
                        sb.append((char) (c - 'a' + 'A'));
                    }
                    dump = "";//clear
                }
                
                if(ascii < 65 || (ascii > 90 && ascii < 97) || ascii > 122) {//not a letter
                    sb.append(str.charAt(i));
                }else {//is a letter
                    if(ascii >= 65 && ascii <= 90) {//uppercase to lowercase
                        sb.append((char) (ascii - 'A' + 'a'));
                    }
                    
                    if(ascii >= 97 && ascii <= 122) {//lowercase to uppercase
                        sb.append((char) (ascii - 'a' + 'A'));
                    }
                }
                
            }else {// Is number
                dump += str.charAt(i);
            }
        }
        
        if(dump.length() != 0) {
            int c = Integer.parseInt(dump);
            
            if(c >= 65 && c <= 90) {//uppercase to lowercase
                sb.append((char) (c - 'A' + 'a'));
            }
            
            if(c >= 97 && c <= 122) {//lowercase to uppercase
                sb.append((char) (c - 'a' + 'A'));
            }
        }
        
        return sb.toString();
    }