Practical Computer Science Concepts Simplified Joshua Silver VP, Product Development Patientco 

Agenda • About me • Approach • Deep dives: – Regex – Finite State Machines – Graph Theory • Overview of other topics 

About Me • CS degree from GA Tech • Helped internationalize CareerBuilder.complatform • Technical co-founder of Patientco • Fun Fact: – Travel junkie: 25 countries by the time I was 25 

About Patientco • Simplifies patient billing for healthcare providers • Bills that patients can actually understand! • Founded in 2009 in Atlanta • Inc. 500 Fastest Growing Company • We’re hiring: http://www.patientcolife.com 

Let’s Go! 

“Don’t reinvent the wheel” 

“Don’t reinvent the wheel” Only works if you know the wheel exists! 

Let’s explore some wheels… 

Regular Expressions ‘Regex’ 

Typical Uses of Regex • Pattern matching within strings • Find & replace • Input Validation • Text filtering 

Regex Example Validate a US phone number. Acceptable format: 000-000-0000 

Regex Example Validate a US phone number. Acceptable formats include: 000-000-0000 (000) 000-0000 

$phoneNumbers = array( "202-555-1234", "1-789-555-0281", "(770) 555-7422", "789 555-7898", "555-8790", "890-000-233", "(789 029-8293", "903.555.1093" ); $regex = '/^(\d{3}\-|\(\d{3}\) )[0-9]{3}-\d{4}$/'; foreach ($phoneNumbers as $phoneNumber) if (preg_match($regex, $phoneNumber) === 1) echo $phoneNumber . ” is valid."; else echo $phoneNumber . ” is NOT valid.”; 

Output: 202-555-1234 is valid. 1-789-555-0281 is NOT valid. (770) 555-7422 is valid. 789 555-7898 is NOT valid. 555-8790 is NOT valid. 890-000-233 is NOT valid. (789 029-8293 is NOT valid. 903.555.1093 is NOT valid. 

$phoneNumbers = array( "202-555-1234", "1-789-555-0281", "(770) 555-7422", "789 555-7898", "555-8790", "890-000-233", "(789 029-8293", "903.555.1093" ); $regex = '/^(\d{3}\-|\(\d{3}\) )[0-9]{3}-\d{4}$/'; foreach ($phoneNumbers as $phoneNumber) if (preg_match($regex, $phoneNumber) === 1) echo $phoneNumber . ” is valid."; else echo $phoneNumber . ” is NOT valid.”; 

$regex = '/^(\d{3}\-|\(\d{3}\) )[0-9]{3}-\d{4}$/'; ^ start of string ( \d{3}\- exactly 3 digits, followed by a - | OR \(\d{3}\) open paren, 3 digits, close paren ) [0-9]{3} alternative notation for 3 digits - \d{4} exactly 4 digits $ end of string 

(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?: \r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:( ?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\0 31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\ ](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+ (?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?: (?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z |(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n) ?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\ r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n) ?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t] )*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])* )(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t] )+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*) *:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+ Regexes  can  get  CRAZY.   Don’t  do  this. **  FROM:    http://www.ex-­‐parrot.com/~pdw/Mail-­‐RFC822-­‐Address.html 

Resources General info: http://en.wikipedia.org/wiki/Regular_expression http://php.net/manual/en/function.preg-match.php http://www.regular-expressions.info/ Online Regex Tester: https://regex101.com/ 

Finite State Machines 

State Machine Example From:  http://en.wikipedia.org/wiki/Finite-­‐state_machine 

No content

Typical Uses of State Machines • Business rules requiring flows – Order management – Payment Processing • Complex parsing applications • Embedded systems • Background-type jobs (“servers”) • Many game engines 

How to implement? 1. Draw a state machine diagram 2. Convert to variable-based state table 3. Implement getStatus() in code 4. Implement transition functions (with error checking) in code 5. PROFIT$$!! 

Order Management System Confirmed Cancelled On  Hold Completed Ready to  ship Order   Created Order Cancelled Card Declined Order Cancelled Card   Successful Card   Successful Order   Shipped Card  Declined 

Order Management System Status timeCancelled timeShipped lastBillingOutcome Confirmed NULL NULL NULL Ready to ship NULL NULL SUCCESS Completed NULL NOT NULL SUCCESS Cancelled NOT NULL NULL -- On Hold NULL NULL DECLINED Confirmed Cancelled On  Hold Completed Ready to  ship 

public function getStatus() { if ($this->timeCancelled === NULL && $this->timeShipped === NULL && $this->lastBillingOutcome === NULL){ return self::ORDER_STATUS_CONFIRMED; } if ($this->timeCancelled === NULL && $this->timeShipped === NULL && $this->lastBillingOutcome === "SUCCESS"){ return self::ORDER_STATUS_READYTOSHIP; } 

public function getStatus() { . . . if ($this->timeCancelled !== NULL && $this->timeShipped === NULL){ return self::ORDER_STATUS_CANCELLED;} if ($this->timeCancelled === NULL && $this->timeShipped === NULL && $this->lastBillingOutcome === "DECLINED"){ return self::ORDER_STATUS_ONHOLD;} handleError("ERROR: INVALID STATUS\n"); } 

public function chargeCard() { if ($this->getStatus() !== self::ORDER_STATUS_CONFIRMED && $this->getStatus() !== ORDER_STATUS_ONHOLD) { handleError("ERROR: Can't charge card - INVALID STATUS\n"); } if (wasCardChargeSuccessful() === true) $this->lastBillingOutcome = "SUCCESS"; else $this->lastBillingOutcome = "DECLINED”; } 

public function ship() { if ($this->getStatus() !== self::ORDER_STATUS_READYTOSHIP) { handleError("ERROR: Can't ship order - INVALID STATUS\n"); } $this->timeShipped = time(); } 

$o1 = new Order(); echo $o1->getStatus(); $o1->chargeCard(); echo $o1->getStatus(); $o1->ship(); echo $o1->getStatus(); -------- Confirmed Ready To Ship Completed 

$o2 = new Order(); echo $o2->getStatus(); $o2->ship(); echo $o2->getStatus(); -------- Confirmed ERROR: Can't ship order- INVALID STATUS 

Why use a state machine? • Business logic self-contained and can be centralized – e.g. If rules for when an order is ready to ship ever change, only need to change a single function. • Complex rules can be implemented simply and compactly • Easier to test 

Related to regex? • Regular Expressions are a specific case of state machine • EVERY regex can be converted to a state machine • State machines can also represent much more complex grammars 

Resources General info: http://en.wikipedia.org/wiki/Automata_theory http://www.i-programmer.info/babbages-bag/223- finite-state-machines.html http://en.wikipedia.org/wiki/Finite-state_machine 

Graph Theory 

No content

No content

No content

What’s a graph? • Set of vertices (the nodes) • Set of edges connecting nodes – Can be directed or undirected – Can optionally be weighted 

Typical Uses of Graphs • More than just “Traveling salesman problem” • Job/resource scheduling • Navigation, maps • Ordering links (eg. Google ranking) • Social graph analysis (eg. Facebook, LinkedIn) • Matching (eg. Dating app) • Indexing, searching 

Graphs are hard easy 1. Determine if the problem is really a graph problem 2. Determine appropriate algorithm 3. Implement algorithm properly 4. TEST! PATTERN RECOGNITION! 

Trees • Directed, connected, acyclic graph • Example: – Binary Search Tree 

Flow • Directed, connected, weighted graph • Flows from a source (s) to a sink (t) 

Bipartite Graphs • Vertices partitioned into 2 sets. Each edge has one endpoint in each set. • Concepts often used: – Vertex cover (node cover) - set of vertices that includes at least one endpoint of each edge – minimum vertex cover - no other vertex cover has fewer vertices. 

Dijkstra's algorithm • Finds the shortest path between nodes in a graph – Directions between cities – Finding cheapest flight – Network packet routing 

Dijkstra's algorithm SFO DFW ORD NYC ATL 70 180 100 30 40 80 80 

Dijkstra's algorithm SFO DFW ORD NYC ATL 70 180 100 30 40 80 80 

Matching • Bipartite graphs used for matching – Match boys / girls on a dating site – Match medical students & residency programs • Implementation – Max-flow min-cut theorem – Hall's marriage theorem 

Social Graph Searching 

Social Graph Searching 

Resources General info: http://en.wikipedia.org/wiki/Graph_(mathematics) http://en.wikipedia.org/wiki/Graph_traversal http://en.wikipedia.org/wiki/Category:Graph_algorithms 

Other common “reinventions” • Mutexes, locks, semaphores – Manage exclusive access of a resource • Queues, Priority Queues – Don’t put them in a DB!!! – Any tasks that can be done asynchronously • Caching – Don’t roll your own – Cache invalidation 

Questions? [email protected] http://www.PatientcoLife.com/