Insert "av" before any Vowel in the given String which is not preceded by another Vowel

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I've written a code which is intended to insert string "av" before any vowel in the given String, which is not be preceded by another vowel.

Consider the String as an input:

"aadeleo"

After adding "av" before each and every vowel which are not preceded by another vowel, the output should be:

"avaadavelaveo"

But my code produces:

"avaavadavelaveavo"

My code:

 public class Main {
    public static void main(String[] args) {
        
        String st = "aadeleo";
        String word = "";
        int l = st.length();
        char c, c2;
        
        for (int i = l - 1; i > 0; i--) {
            c = st.charAt(i);
            c2 = st.charAt(i - 1);
            
            if ((c == 'a' || c == 'e' ||
                c == 'i' || c == 'o' ||
                c == 'u') && (c2 != 'a' || c2 != 'e' ||
                c2 != 'i' || c2 != 'o' ||
                c2 != 'u')) {
                word = "av" + c + word;
            } else
                word = c + word;
        }
        c = st.charAt(0);
        
        if (c == 'a' || c == 'e' ||
            c == 'i' || c == 'o' ||
            c == 'u')
            word = "av" + c + word;
        else
            word = c + word;
        
        System.out.println(word);
    }
}
algorithm java string
1 Answers

There's no need to double-check the previous character since it has already been seen.

The logic for determining whether a character is a vowel can be extracted into a separate method, that would make the code more readable. To perform this check, we can use String.indexOf(char) method instead of a swarm of conditions.

And it's highly advisable to avoid string-concatenation when you're not sure how many times it might take place. The better option would be to use StringBuidler.

That's how it might be implemented:

public static String insertBeforeNonPrecededVowel(String str, String insert) {
    
    StringBuilder result = new StringBuilder();
    boolean isPrecededByVowel = false;
    
    for (int i = 0; i < str.length(); i++) {
        char next = str.charAt(i);
        boolean nextIsVowel = isVowel(next);
        
        if (nextIsVowel && !isPrecededByVowel) result.append(insert); // if current character is Vowel, and it's not preceded by Vowel
        
        isPrecededByVowel = nextIsVowel;
        result.append(next);
    }
    return result.toString();
}

public static boolean isVowel(char ch) {
    
    return "aeiou".indexOf(ch) != -1;
}

main()

public static void main(String[] args) {
    System.out.println(insertBeforeNonPrecededVowel("aadeleo", "av"));
}

Output:

avaadavelaveo
user_179499450
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