Recursion/PairStar.java at main · hamhus/Recursion · GitHub

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//https://codingbat.com/prob/p158175
/*Given a string, compute recursively a new string where identical chars that are adjacent in the original string are separated from each other by a "*".


pairStar("hello") → "hel*lo"
pairStar("xxyy") → "x*xy*y"
pairStar("aaaa") → "a*a*a*a"*/

public String pairStar(String str) {
  if(str.length()==0) return "";
  if(str.length()==1) return str;

  //if(str.substring(0,1).equals(str.substring(1,2)))
    //return str.substring(0,1)+"*"+pairStar(str.substring(1));
  //return str.substring(0,1)+pairStar(str.substring(1));

  //OR

  return (str.substring(0,1).equals(str.substring(1,2)))?
        str.substring(0,1)+"*"+pairStar(str.substring(1)):str.substring(0,1)+pairStar(str.substring(1));
}