Doubling one letter with each new occurence

so I have task to double number of letter “a” every time it occurs in a string. For example sentence “a cat walked on the road” , at the end must be “aa caaaat waaaaaaaalked on the roaaaaaaaaaaaaaaaa” . I had something like this on my mind but it doubles every charachter, not only “a”.

    public static void main(String[] args) {
    String s = "a bear walked on the road";
    String result = "";
    int i = 0;
    while(i<s.length()){
        char a = s.charAt(i);
        result = result + a + a;
        i++;
    }
    System.out.println(result);
}

Answer

You need to check what the char a is (in your case, ‘a’). Additionally, you do not repeat the characters more than twice in your code, hence not getting the answer you expected: result = result + a + a only adds ‘a’ twice, not giving you: “aa caaaat waaaaaaaalked…”.

Here is the solution:

public static void main(String[] args) {
    String s = "a bear walked on the road";
    String result = "";
    char lookingFor = 'a'; // Can change this to whatever is needed
    int counter = 2;
    for (int i = 0; i < s.length(); i++) {
        if (s.charAt(i) == lookingFor) { // The current character is what we need to be repeated.
            
            // Repeat the character as many times as counter is (each loop: 2, 4, 6, 8, ...)
            for (int j = 0; j < counter; j++) {
                result += lookingFor;
            }

            counter *= 2; // Double counter at every instance of 'a'
        }
        else { // The current char is not what we are looking for, so we just add it to our result.
            result += s.charAt(i);
        }
    }
    System.out.println(result);
}