Java recursion #4

jr4.java

/* Given a string and a non-empty substring sub, compute recursively
the number of times that sub appears in the string, without the sub
strings overlapping. */

public int strCount(String str, String sub) {
  if (str.length() < sub.length()) return 0;
  if (str.substring(0, sub.length()).equals(sub) &&
     !str.substring(sub.length(), sub.length()).equals(sub))
  {
      return 1 + strCount(str.substring(sub.length()), sub);
  }
  return strCount(str.substring(1), sub);
}

/* 
Given a string and a non-empty substring sub, compute recursively
if at least n copies of sub appear in the string somewhere, possibly
with overlapping. N will be non-negative. */

public boolean strCopies(String str, String sub, int n) {
  if (n == 0)
    return true;
  if (str.length() < sub.length())
    return false;
  if (str.substring(0, sub.length()).equals(sub))
    return strCopies(str.substring(1), sub, n - 1);
  return strCopies(str.substring(1), sub, n);
}