Simple pattern matching between two string inputs using Java (Google interview challenge)












0












$begingroup$


The interview question is:




Write a function isMatch (without using java.util.Regex) that takes two strings as arguments:





  • s (a string to match), and


  • p (a regular expression pattern).


It should return a Boolean denoting whether s matches p.



p can be composed of alphabetic characters and '*' (denoting that the previous character matches 0 or more times).




This is the code I have written:



    private boolean isNextCharStarred(String s) {
return s.length() >= 2 && s.charAt(1) == '*';
}

private boolean recIsMatch(String s, String p, boolean hasPatternBeenEaten) {
if (p.length() == 0) {
return true;
}
if (s.length() == 0) {
if (isNextCharStarred(p)) {
return recIsMatch(s, p.substring(2), true);
}
return p.length() == 0;
}
if (isNextCharStarred(p)) {
if (s.charAt(0) != p.charAt(0)) {
return recIsMatch(s, p.substring(2), true);
}
return recIsMatch(s.substring(1), p, hasPatternBeenEaten)
|| recIsMatch(s, p.substring(2), true);
}
if (s.charAt(0) == p.charAt(0)) {
return recIsMatch(s.substring(1), p.substring(1), true);
}
if (hasPatternBeenEaten) {
return false;
}
return recIsMatch(s.substring(1), p, hasPatternBeenEaten);
}

public boolean isMatch(String s, String p) {
return recIsMatch(s, p, false);
}


Are there any bugs? How could it be improved?










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    0












    $begingroup$


    The interview question is:




    Write a function isMatch (without using java.util.Regex) that takes two strings as arguments:





    • s (a string to match), and


    • p (a regular expression pattern).


    It should return a Boolean denoting whether s matches p.



    p can be composed of alphabetic characters and '*' (denoting that the previous character matches 0 or more times).




    This is the code I have written:



        private boolean isNextCharStarred(String s) {
    return s.length() >= 2 && s.charAt(1) == '*';
    }

    private boolean recIsMatch(String s, String p, boolean hasPatternBeenEaten) {
    if (p.length() == 0) {
    return true;
    }
    if (s.length() == 0) {
    if (isNextCharStarred(p)) {
    return recIsMatch(s, p.substring(2), true);
    }
    return p.length() == 0;
    }
    if (isNextCharStarred(p)) {
    if (s.charAt(0) != p.charAt(0)) {
    return recIsMatch(s, p.substring(2), true);
    }
    return recIsMatch(s.substring(1), p, hasPatternBeenEaten)
    || recIsMatch(s, p.substring(2), true);
    }
    if (s.charAt(0) == p.charAt(0)) {
    return recIsMatch(s.substring(1), p.substring(1), true);
    }
    if (hasPatternBeenEaten) {
    return false;
    }
    return recIsMatch(s.substring(1), p, hasPatternBeenEaten);
    }

    public boolean isMatch(String s, String p) {
    return recIsMatch(s, p, false);
    }


    Are there any bugs? How could it be improved?










    share|improve this question









    New contributor




    MFX is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.







    $endgroup$















      0












      0








      0





      $begingroup$


      The interview question is:




      Write a function isMatch (without using java.util.Regex) that takes two strings as arguments:





      • s (a string to match), and


      • p (a regular expression pattern).


      It should return a Boolean denoting whether s matches p.



      p can be composed of alphabetic characters and '*' (denoting that the previous character matches 0 or more times).




      This is the code I have written:



          private boolean isNextCharStarred(String s) {
      return s.length() >= 2 && s.charAt(1) == '*';
      }

      private boolean recIsMatch(String s, String p, boolean hasPatternBeenEaten) {
      if (p.length() == 0) {
      return true;
      }
      if (s.length() == 0) {
      if (isNextCharStarred(p)) {
      return recIsMatch(s, p.substring(2), true);
      }
      return p.length() == 0;
      }
      if (isNextCharStarred(p)) {
      if (s.charAt(0) != p.charAt(0)) {
      return recIsMatch(s, p.substring(2), true);
      }
      return recIsMatch(s.substring(1), p, hasPatternBeenEaten)
      || recIsMatch(s, p.substring(2), true);
      }
      if (s.charAt(0) == p.charAt(0)) {
      return recIsMatch(s.substring(1), p.substring(1), true);
      }
      if (hasPatternBeenEaten) {
      return false;
      }
      return recIsMatch(s.substring(1), p, hasPatternBeenEaten);
      }

      public boolean isMatch(String s, String p) {
      return recIsMatch(s, p, false);
      }


      Are there any bugs? How could it be improved?










      share|improve this question









      New contributor




      MFX is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$




      The interview question is:




      Write a function isMatch (without using java.util.Regex) that takes two strings as arguments:





      • s (a string to match), and


      • p (a regular expression pattern).


      It should return a Boolean denoting whether s matches p.



      p can be composed of alphabetic characters and '*' (denoting that the previous character matches 0 or more times).




      This is the code I have written:



          private boolean isNextCharStarred(String s) {
      return s.length() >= 2 && s.charAt(1) == '*';
      }

      private boolean recIsMatch(String s, String p, boolean hasPatternBeenEaten) {
      if (p.length() == 0) {
      return true;
      }
      if (s.length() == 0) {
      if (isNextCharStarred(p)) {
      return recIsMatch(s, p.substring(2), true);
      }
      return p.length() == 0;
      }
      if (isNextCharStarred(p)) {
      if (s.charAt(0) != p.charAt(0)) {
      return recIsMatch(s, p.substring(2), true);
      }
      return recIsMatch(s.substring(1), p, hasPatternBeenEaten)
      || recIsMatch(s, p.substring(2), true);
      }
      if (s.charAt(0) == p.charAt(0)) {
      return recIsMatch(s.substring(1), p.substring(1), true);
      }
      if (hasPatternBeenEaten) {
      return false;
      }
      return recIsMatch(s.substring(1), p, hasPatternBeenEaten);
      }

      public boolean isMatch(String s, String p) {
      return recIsMatch(s, p, false);
      }


      Are there any bugs? How could it be improved?







      java strings interview-questions reinventing-the-wheel






      share|improve this question









      New contributor




      MFX is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question









      New contributor




      MFX is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question








      edited 8 mins ago









      Cody Gray

      3,433926




      3,433926






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      asked 4 hours ago









      MFXMFX

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      1




      New contributor




      MFX is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      New contributor





      MFX is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






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      Check out our Code of Conduct.






















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