/* Given a string, compute recursively (no loops) a new string where all * appearances of "pi" have been replaced by "3.14". */ public String changePi(String str) { if(str.length() <= 1) return str; if(str.substring(0, 2).equals("pi")) return "3.14" + changePi(str.substring(2)); return str.charAt(0) + changePi(str.substring(1)); }