EJ Exercises with explanations

ej_exercises.js

/* 4.4 deep linking

*/

function deepEqual(a, b) {
  if (a === b) return true;
  
  if (a == null || typeof a != "object" ||
      b == null || typeof b != "object")
    return false;
  
  var propsInA = 0, propsInB = 0;

  for (var prop in a)
    propsInA += 1;

  for (var prop in b) {
    propsInB += 1;
    if (!(prop in a) || !deepEqual(a[prop], b[prop]))
      return false;
  }

  return propsInA == propsInB;
}

var obj = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj, obj));
// → true
console.log(deepEqual(obj, {here: 1, object: 2}));
// → false
console.log(deepEqual(obj, {here: {is: "an"}, object: 2}));
// → true


/* 4.3 a list
function arrayToList takes arg array. Make var list null.
Loop over the arrays length, be sure to minus the counter! 
List should be an object, with value set to array index, rest is recursive executing list.
Return list.
function listToArray takes arg list. Var array empty.
Loop over var node, and node equals list, counter is node.rest.
Push the node.value, return the array.
function prepend takes value and list args. Return the object value and rest list.
function nth takes args list, n. 
Check if !list return undefined. Else if n == 0, return list.value.
Else return recursive nth function list.rest and n -1.
*/

function arrayToList(array) {
  var list = null;
  for (var i = array.length - 1; i >= 0; i--)
    list = {value: array[i], rest: list};
  return list;
}

function listToArray(list) {
  var array = [];
  for (var node = list; node; node = node.rest)
    array.push(node.value);
  return array;
}

function prepend(value, list) {
  return {value: value, rest: list};
}

function nth(list, n) {
  if (!list)
    return undefined;
  else if (n == 0)
    return list.value;
  else
    return nth(list.rest, n - 1);
}

console.log(arrayToList([10, 20]));
// → {value: 10, rest: {value: 20, rest: null}}
console.log(listToArray(arrayToList([10, 20, 30])));
// → [10, 20, 30]
console.log(prepend(10, prepend(20, null)));
// → {value: 10, rest: {value: 20, rest: null}}
console.log(nth(arrayToList([10, 20, 30]), 1));
// → 20



/* 4.2 reversing an array
New array Method: create function reverseArray with one arg.
create new var output to hold the new array. 
Start the Loop var i equal to array.length -1, decrease i NOT increase. (you start from the last array num).
push to output the array[i]. Return ouptut. 
Same array Method:
In the loop find the middle integer using math.floor and divide array length by 2.
Make new var point to current array[i].
Make the array[i] point to the array[array.length] minus 1, -i.
Point old to the array[array.length -1, -i]
*/

function reverseArray(array) {
  var output = [];
  for (var i = array.length - 1; i >= 0; i--)
    output.push(array[i]);
  return output;
}

function reverseArrayInPlace(array) {
  for (var i = 0; i < Math.floor(array.length / 2); i++) {
    var old = array[i];
    array[i] = array[array.length - 1 - i];
    array[array.length - 1 - i] = old;
  }
  return array;
}

console.log(reverseArray(["A", "B", "C"]));
// → ["C", "B", "A"];
var arrayValue = [1, 2, 3, 4, 5];
reverseArrayInPlace(arrayValue);
console.log(arrayValue);
// → [5, 4, 3, 2, 1]


// 4.1 sum of a range
/*____________________________
Create function with 3 args, start, end, step. If the step is null make the step 1.
Create array[]. If the step > 0 then loop the var i and increase i += step. 
Push (i) to the array. Repeat for Else. Return the array.
Function sum requires 1 arg - array. Add a total counter set to 0.
Loop over array.length and add the total of the array[i]. return total.
*/

function range(start, end, step) {
  if (step == null) step = 1;
  var array = [];

  if (step > 0) {
    for (var i = start; i <= end; i += step)
      array.push(i);
  } else {
    for (var i = start; i >= end; i += step)
      array.push(i);
  }
  return array;
}

function sum(array) {
  var total = 0;
  for (var i = 0; i < array.length; i++)
    total += array[i];
  return total;
}

console.log(sum(range(1, 10)));
// → 55
console.log(range(5, 2, -1));
// → [5, 4, 3, 2]


// 3.3 Bean counting
/*____________________________
Create function with 2 args, then counter. 
For loop the string.length and if the string.chartAt = the arg, increase the counter
With countBs, return the other function and assign B as the arg.
*/

function countChar(string, ch) {
  var counted = 0;
  for (var i = 0; i < string.length; i++)
    if (string.charAt(i) == ch)
      counted += 1;
  return counted;
}

function countBs(string) {
  return countChar(string, "B");
}


// 3.2 Recursion
/*____________________________
Create four conditional if statements. 
2 Conditionals check if the remainder is 0 (true) or 1 (false)
2 Conditionals are recursive and execute the function loop again until n = 0 or 1
*/

function isEven(n) {
  if (n == 0)
    return true;
  else if (n == 1)
    return false;
  else if (n < 0)
    return isEven(-n);
  else
    return isEven(n - 2);
}


// 3.1 return smallest number
/* ____________________________
return  Math.min method on args */

function min(a, b) {
  return Math.min(a, b);
}

// 2.3 Chess board
/*____________________________
 Create vars Size and blank string Board. 
 Make two for loops contained within each other, loop X contains loop Y.
 If x and y leaves % 2 == 0, then increase with blank or else add #
 After y loop exits, add line break for board then console board.
*/

var size = 8;
var board = "";

for (var x = 0; x < size; x++) {
 for (var y = 0; y < size; y++) {
 	if((x + y) % 2 == 0)
      board += " ";
    else
     board += "#";
 }
 board += "\n";
}

console.log(board);

// 2.2 FizzBuzz loop with exceptions. 
/*____________________________
for loop less than 100, with a counter increase of 1
Create empty var string, then create two if conditions to check 3 and 5 % = 0. Do not use else if becuase it will overide FizzBuzz.
console the output or the number 
*/

for (var n = 0; n < 100; n++) {
  var output = "";
  if (n % 3 == 0)
    output += "Fizz"
  if (n % 5 == 0)
    output += "Buzz"
  console.log(output || n);
}


// 2.1 Loop a triangle
/*____________________________
create var, line length less than 8, then increase by one
*/

for (var line = "#"; line.length < 8; line += "#")
console.log(line);