Question

I am attempting to use recursion to reverse a string but the special twist is that I must start at a specified index return that character contained at the index and then reverse the remaining string after that index and combine the two into one output. I have tried to do this and sometimes it gives an array out of bounds exception and sometimes ends up with more letters than it should have such as this test of helloooo coming out as lloooooo. Any help with tweaking this code would be appreciated as I became really lost when the need for the second parameter was known to me.

  public class ReverseTest
    {
        public static void main(String[] argv) 
        {
            System.out.println(reverse("a", 0));
            System.out.println(reverse("hi", 0));
            System.out.println(reverse("helloooo", 2));
        }


        public final static String reverse(String s, int ind)
        {
            int length = s.length(); //get string length

            if (length <= 1) //if length is 1 or lower just repeat the string nothing to do
                return s; //return string
            else //if we have something to work with...
                return s.substring(ind) + reverse(s.substring(ind + 1, length - 1), ind); //return substring of necessary index + reverse the rest and display in one string
        }
    }

Answer 1

Not sure what is wrong with your version, but I built my own according to what I find to be an intuitive implementation:

private static String reversePartially(String initial, int target) {
    return reversePartially(initial, target, target);
}

private static String reversePartially(String initial, int index, int target) {
    // if we are at the target index put the character at the front
    if(index == target) return initial.charAt(target) + reversePartially(initial, index + 1, target);
    // if we are in the second part return the characters reversed
    if(index > target) return reversePartially(initial, index + 1, target) + initial.charAt(index);
    // base condition
    if(index == initial.length()) return "";
    return "";
}