[CREDITS HERE]

Intro to

Algorithms:
Day 1

Recursion & Pseudoclasses

Stacks & Queues

[preface stuff]

  • Agenda?
  • Class format?
  • FAQs?

Recursion

Call Yourself

function callMyself() {

  callMyself();

}

What if you do a Google search for recursion?

General Algorithm

function callMyself() {

  if() {
    // base case
    return;
  } else {
    // recursive case
    callMyself();
  }
    
  return;
}
  1. Identify base case
  2. Identify recursive cases
  3. Write procedures for each case

Advice: Use a bottom-up approach by looking for patterns by starting with small or first few cases

Example: Factorial

function computeFactorial(num) {
  var result = 1;

  for(var i = 2; i <= num; i++) {
    result *= i;
  }

  return result;
}
results *= 2;
results *= 3;
results *= 4;
results *= 5;

If we call computeFactorial(5), then the loop will run:

Example: Factorial

function computeFactorial(num) {
  if(num === 1) {
    return 1;
  } else {
    return num * computeFactorial(num - 1);
  }
}
5 * computeFactorial(4)
    4 * computeFactorial(3)
        3 * computeFactorial(2)
            2 * computeFactorial(1)
                1

If we call computeFactorial(5), then the recursion will run:

function logNumbers(start, end) {
  for(var i = start; i <= end; i++) {
    console.log(i);
  }
}

function logNumbersRecursively(start, end) {
  function recurse(i) {
    console.log(i);

    if(i < end) {
      recurse(i + 1);
    }
  }

  recurse(start);
}

Converting a loop into recursion

Exercises!

(but first, a quick overview)

Pseudoclasses

function MyClass(input) {

  this.myProp = input;

}
MyClass.prototype.myMethod = function() {
  console.log('Check it out: ' + this.myProp);
};

Syntax

Constructor

Properties

(per instance)

Defining a (pseudo)Class

Methods (for all instances)

function MyClass(input) {
}

Syntax

Using a (pseudo)Class

var myInstance = new MyClass('hello');

var myOtherInstance = new MyClass('bye');

myInstance.myMethod();

myOtherInstance.myMethod();

The results of the shared method depend on the unique instance properties

Data Structures:
Stacks

Stacks

Description

Stacks

The last item added into the stack will be the first one taken out of the stack.
(aka LIFO)

Description

(aka pushed onto)

(aka popped off)

Stacks

Example Use Cases

  • Backtracking / History
    i.e., Hitting the back + forward
    buttons of your web browser
     
  • Call stack

Data Structures:
Queues

Queues

Description

[ TODO: Find diagram that is legal for commercial use ]

Queues

The first item added into the queue will be the first one taken out of the queue.
(aka FIFO)

Description

(aka enqueued)

(aka dequeued)

Queues

Example Use Cases

  • JavaScript's Event Queue
     
  • Message Queueing
    e.g., RabbitMQ

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