// Write a function called `containsTwice` that accepts a number and an array,

// and returns `true` if that number appears in the array twice, and `false`

// otherwise.

//

// containsTwice(5, [1, 2, 3, 4, 5]);

// //=> false

//

// containsTwice("hello", [ "hello", "world", "hello" ]);

// //=> true

//

// containsTwice(true, [ true, false, false, true ]);

// //=> true

//

// containsTwice(10, [10, 10, 10, 10, 10]);

// //=> false

//

var containsTwice = function () {

};

// Generalize the previous solution into a function called `containsNTimes` so

// that it can check for a value an arbitrary number of times.

//

// containsNTimes(3, "hello", [ "hello", "hello", "hello" ]);

// //=> true

//

// containsNTimes(5, true, [ true, true, true, true, false ]);

// //=> false

//

// containsNTimes(0, 5, [ 1, 2, 3, 4, 5 ]);

// //=> false

//

var containsNTimes = function () {

};

// Write a function called `atLeastOneEven` that returns `true` if at least one of

// the numbers in input array is even, false otherwise. It should throw an error if

// the argument is not an array.

//

// atLeastOneEven([ 3, 5, 6, 7, 9 ]);

// //=> true

//

// atLeastOneEven([]);

// //=> false

//

// atLeastOneEven([ 101, 203, 401 ]);

// //=> false

//

// atLeastOneEven("hello");

// //=> input should be an array!

//

var atLeastOneEven = function () {

};

// Write a function called `allStrings` that accepts an array as an argument and

// returns `true` if all of the values in the array are strings. It should

// return false if they are not all strings, and throw an error if the input is

// not an array.

//

// allStrings([ "these", "are", "all", "strings" ]); //=> true

//

// allStrings([ "these", "are", "not", 5 ]); //=> false

//

// allStrings([ ]); //=> true

//

// allStrings("hello"); //=> input should be an array!

//

// Although the tests will not be checking for this, try to make your loop exit

// as soon as it finds a non-string entry in the array.

//

var allStrings = function () {

};

// Write a function that accepts two arrays, and returns true if any of the

// values in the first array appear twice in the second array. You might want to

// reuse the function `containsNTimes` or `containsTwice` from above. It should

// throw an error if either of the inputs are not arrays.

//

//

// containsAnyTwice([1, 2], ["hello", 1, "world", 1]);

// //=> true

//

// containsAnyTwice([], ["always", "will", "return", "false"]);

// //=> false

//

// containsAnyTwice(["hello", "world"], ["hello", "hello", "world", "world"]);

// //=> true

//

// containsAnyTwice("hello", ["hello", "world"]);

// //=> containsAnyTwice expects two arguments, both of which should be an array.

//

// Although the tests will not be checking for this, try to make your loop exit

// as soon as it finds an element in the first array that appears twice in the second

// array.

//

var containsAnyTwice = function () {

};

// In the previous problem, we determined whether or not an array contains any

// of a list of values exactly twice. In this problem, we'll actually return

// those values appearing twice. Create a new function that returns an array of

// only the values from the first array that appear twice in the second array.

//

// For this problem, you'll create a new array, and you'll use its `push`

// function to add elements to the end. You'll most likely want to use the

// `containsTwice` function you created in the previous exercise.

//

// The difficulty here will be in avoiding duplicates. You may want to use the

// `indexOf` method of the resulting array to confirm that you're not adding a

// value a second time.

//

// getValuesAppearingTwice(["hello", 1, "world", 1]);

// //=> [ 1 ]

//

// getValuesAppearingTwice(["always", "will", "return", "empty"]);

// //=> []

//

// getValuesAppearingTwice(["hello", "hello", "world", "world", "goodbye"]);

// //=> [ "hello", "world" ]

//

// getValuesAppearingTwice(["hello", "world", "goodbye"])

// //=> []

//

var getValuesAppearingTwice = function () {

};

// Using a standard `for` loop, along with the `push` function, write a function

// called `range` that accepts two numbers, `begin` and `end`, and returns an array

// that contains all of the integers starting at `begin` and ending at `end`

// (including `begin` and `end`). For example:

//

// range(5,10);

// //=> [5, 6, 7, 8, 9, 10]

//

// range(0,3);

// //=> [0, 1, 2, 3]

//

// range(10,3);

// //=> [10, 9, 8, 7, 6, 5, 4, 3]

//

// It should throw an error when either of the arguments are not numbers.

//

// range("hello", "world");

// //=> arguments to range must be numbers

//

var range = function () {

};

// Using the `isHTMLElement` and `getTagName` function from one of the previous

// sections, write a function called `mapToTags` that accepts an array of HTML

// elements and returns a new array that consists of only the tags associated with

// those HTML elements. It should throw an error if any of the elements are not

// HTML elements, or if the input is not an array.

//

// mapToTags(["<p>this is a paragraph</p>", "<span>this is a span</span>", "<li>this is a list item</li>"]);

// //=> ["p", "span", "li"]

//

// mapToTags([]);

// //=> []

//

// mapToTags(["<p>this is a paragraph</p>", "this is a tweet"]);

// //=> "this is a tweet" is not an HTML element!

//

// mapToTags(5);

// //=> wat?

//

// mapToTags([ "not an html element" ]);

// //=> all entries must be html elements!

//

var mapToTags = function () {

};

// Write a function called `filterToLol` which accepts an array of tweets and

// returns an array that consists only of those that contain `lol` (upper, lower,

// or mixed-case). It should throw an error if the input is not an array or if any

// of the elements are not strings.

//

// filterToLol(["hello world!", "this is a tweet lol", "this is a tweet omg"]);

// //=> ["this is a tweet lol"]

//

// filterToLol(["lol", "LOL", "LoL", "omg", "lollerskates"]);

// //=> ["lol", "LOL", "LoL", "lollerskates"]

//

// filterToLol(["omg", "this is a tweet"]);

// //=> []

//

// filterToLol(5);

// //=> no can do.

//

// filterToLol(["this is a string", false, 5]);

// //=> all entries must be strings!

//

var filterToLol = function () {

};