用递归重复一个字符串，初学者

Question

I'm supposed to write a simple method that returns given string for given amount, seperated by comma (and no comma in the end), with recursion. If there are less than two counts, the return is empty string "".

final static String COMMA = ", ";
public static String replicate(String s, int count) {
    String answer = "";
    if (count < 2) {
        return answer;
    }
    else {
        answer = s + COMMA + replicate(s, (count - 1));
        return answer;
    }
}

If I put s = cat and count = 5, I get cat, cat, cat, cat, - One short what I need. I'm at my wits end here what to do, to get proper amount of repeats here without the comma at the end.

EDIT: Clearly I failed to communicate, that the method SHOULD return an empty string, if the count is two or less. Sorry for the lack of clarity there.

Answer 1

You're extremely close! When you hit your base case count < 2 , instead of returning an empty string, you can return your input string. Be sure to check that length isn't 0, too.

EDIT: from information in the comments, you want to return an empty string for any counts less than or equal to two. Odd requirement, but this will fit that issue; it uses three as a base case instead of two, returning three s inputs concatenated together.

  final static String COMMA = ", ";
  public static String replicate(String s, int count) {
      String answer = "";
      if(count <= 2) {
        return answer;
      }
      if(count == 3) {
        return (s + COMMA + s + COMMA + s);
      }
      else {
          answer = s + COMMA + replicate(s, (count - 1));
          return answer;
      }
  }

Demo

Answer 2

Every element is there, just a bit unreadable code.

• If count is 0, "".
• If one, s itself.
• Otherwise s, + recursive result.

So:

public static String replicate(String s, int count) {
    if (count <= 0) {
        return "";
    } else if (count == 1) {
        return s;
    } else {
        return s + COMMA + replicate(s, count - 1);
    }
}

What lead to mental failure was the variable answer, and the two cases of < 2 .

Answer 3

public static String replicate(String s, int count) {

    if (count >= 2) {
        s = s + COMMA + replicate(s, --count);
    }
    return s;
}

replicate("hii", 4) --> return "hii,hii, hii, hii"

COMMA + replicate("hii", 3) --> return "hii, hii, hii" COMMA + replicate("hii", 2) --> return "hii, hii" COMMA + replicate("hii", 1) --> return "hii"