Front-end Algorithm Scripting – Page 2

FCC ‘Title Case A Sentence’

Today we’re going to work through another of freeCodeCamp’s Basic Algorithm Scripting challenges – ‘Title Case A Sentence’. To solve this challenge we must write a function that accepts a string, then returns that string with the first letter of each word capitalized and the remainder of each word in lowercase.

We’ll be using concepts that we’ve covered in previous posts (i.e. for loops, string methods, and arrays) and adding a couple new things like method chaining and some new string methods.

As I’ve mentioned previously, in JavaScript, the data type String has many methods associated with it. W3schools has a good intro to these methods, MDN covers the string object on a deeper level.

Here’s the starting point given to us by freeCodeCamp.

function titleCase(str) {
  return str;
}

titleCase("I'm a little tea pot");

function titleCase(str) {

return str;

}

titleCase("I'm a little tea pot");

We’ll start solving this challenge by breaking the given string (str) into an array of words, the same way we started ‘Find the Longest Word in a String’.

  var wordArray = str.split(" ");

1	var wordArray = str.split(" ");

Quick tangent – we haven’t discussed yet that JavaScript can be tested right in your browser. If you have a question about what a snippet of code does, just plug it into the console of your browser and test it. To make sure the str.split() method that I just created is doing what I want, I plugged it into the console in Chrome and tested it.

var str = "I'm a little tea pot";
var wordArray = str.split(' ');
console.log(wordArray);
["I'm", "a", "little", "tea", "pot"]

var str = "I'm a little tea pot";

var wordArray = str.split(' ');

console.log(wordArray);

["I'm", "a", "little", "tea", "pot"]

As you can see, str.split(‘ ‘) is splitting the given string into an array, with each word as an individual element. Now I’m confident in continuing with the solution to the algorithm challenge…

Next, we need to iterate through the array and capitalize the first letter of each word and lowercase the rest of the word. To iterate through the array, we’ll use a for loop. To handle the upper/lowercasing of the words, we’ll need a couple new string methods.

For a deeper understanding, and a list of many more string methods, check out the MDN page on strings. Today, we’ll be using charAt(), toUpperCase(), toLowerCase() and slice().

toUpperCase() and toLowerCase() do exactly what they sound like, they return the calling string value in upper and lower cases respectively. charAt() allows you to access a specific character of a string and takes one parameter – the index of the character you want to access (indexes of strings start at 0, just like arrays).

slice() allows you to access a specific segment of a string. It takes two arguments, the indexes of where you want the segment to start and finish. The second parameter is optional, if you leave it out, the slice will start at the first index you provide and continue to the end of the string. Very important – all four methods mentioned above return the value of a string, they do not change the calling string. See code below for demonstration…

var str = "I'm a little tea pot";
var newStr = str.slice(3);
console.log(str);
I'm a little tea pot //original string (str) unchanged by slice()
console.log(newStr);
 a little tea pot    //slice starting at index(3) was returned to newStr

var str = "I'm a little tea pot";

var newStr = str.slice(3);

console.log(str);

I'm a little tea pot //original string (str) unchanged by slice()

console.log(newStr);

a little tea pot //slice starting at index(3) was returned to newStr

Now, as mentioned above, we can chain these methods together using dot notation, so that after one method is called, a second method is called on the returned string of the first.

var str = 'test';
var newStr = str.charAt(0).toUpperCase();
console.log(str);
test         //again, original string left unchanged
console.log(newStr);
T            //toUpperCase was called on charAt(0) and returned to newStr

var str = 'test';

var newStr = str.charAt(0).toUpperCase();

console.log(str);

test //again, original string left unchanged

console.log(newStr);

T //toUpperCase was called on charAt(0) and returned to newStr

Check out this post on method chaining for a better understanding.

We can use everything we’ve talked about to get the first character of a string and capitalize it, then get the rest of the string (starting at index 1) and lowercase it. Putting it all together looks like this:

function titleCase(str) {
  //create an array to hold each word in the string
  var wordArray = str.split(" ");
  //loop through each element of the array
  //capitilize the first character of each word, lowercase rest of word
  for (var i = 0; i < wordArray.length; i++){
    wordArray[i] = wordArray[i].charAt(0).toUpperCase() + wordArray[i].slice(1).toLowerCase();
  }
  //turn array back into string and return  
  return wordArray.join(" ");
}

function titleCase(str) {

//create an array to hold each word in the string

var wordArray = str.split(" ");

//loop through each element of the array

//capitilize the first character of each word, lowercase rest of word

for (var i = 0; i < wordArray.length; i++){

wordArray[i] = wordArray[i].charAt(0).toUpperCase() + wordArray[i].slice(1).toLowerCase();

}

//turn array back into string and return

return wordArray.join(" ");

}

Several notes on the above solution…

We used the join() method, which does the exact opposite of split. join() is an array method that returns a string delimited by what you pass as an argument. In this case, we gave an empty space (” “) as the argument, so each element of the array was joined together separated by a space.

Also, you will note that we used a ‘+’ to connect 2 parts of a string together. This is an easy way in JavaScript to build a string. It can be used with both literal strings and variables as such:

var a = 'this'
var b = 'you ' + 'can ' + 'connect ' + 'strings ' + 'like ' + a;
console.log(b);
you can connect strings like this

var a = 'this'

var b = 'you ' + 'can ' + 'connect ' + 'strings ' + 'like ' + a;

console.log(b);

you can connect strings like this

Hopefully this straightened out the code for you… See you next time.

-Jeremy

FCC ‘Find the Longest Word in a String’

The next freeCodeCamp algorithm that we’ll work on here at The Crooked Code will be ‘Find the Longest Word in a String’. The challenge here is to write a function that accepts a string as a parameter and returns the length of the longest word in the string, which means we’ll be returning a number.

Before we start on the algorithm, there are a few JavaScript concepts that we’ll need to go over…

In JavaScript, methods are functions that are stored as object properties. Further, there are many methods that are built into JavaScript that are available to manipulate things like strings and arrays. This algorithm will let us start exploring the methods associated with these various data types. This concept might not seem immediately clear, however, this w3schools page explains the concept in a little more detail, or just keep reading this post and things should clear up.

As is the case with accessing other properties of objects, we can use dot notation to call these methods.

Let’s try to clear things up with an example:

String.split() is one of many methods that can be used on a string. Split() will divide a string into an array of substrings. It takes up to two arguments. The first argument is the separator, or where the string will be divided. The second argument is the limit and is optional. The limit is a number specifying the max number of substrings (we won’t be using this second argument is this example). In use, split() looks something like this:

var str = 'this is a string';
var arrOfStr = str.split(' ');

console.log(arrOfStr);
["this", "is", "a", "string"]

var str = 'this is a string';

var arrOfStr = str.split(' ');

console.log(arrOfStr);

["this", "is", "a", "string"]

A few things to note in this code… We passed (‘ ‘) to str.split which means str will be divided into substrings at each whitespace. (if you pass (”) str will be split at every letter, if you pass ‘,’ it’ll be split at every comma and so on..). Also, console.log() is an excellent way of checking that your code is doing what you want. In this case, we passed it the array of strings (arrOfStr) in which we stored all the substrings so we could check if the code was doing what we intended. As you can see from the line below the console.log call, arrOfStr now contains 4 different strings, 1 for each word in the original string (str).

One more quick thing to cover before we get into solving the algorithm – arrays. An array is a data structure that allows us to store a list of multiple values in a single variable. Each value in the list is called an element and can be accessed individually using bracket notation, which is also explained in this MDN page. An example using bracket notation with the above example would be:

console.log(arrOfStr[0]);
this

1 2	console.log(arrOfStr[0]); this

As you can see, the index (the number inside the bracket notation that accesses an individual element in the array) of the first element of an array is 0. Therefore, when we log index 0 of arrOfStr to the console we get ‘this’. A good intro to arrays can be found here.

Ok, now moving onto the problem at hand…

FCC provides the following starting point:

function findLongestWord(str) {
  return str.length;
}

findLongestWord("The quick brown fox jumped over the lazy dog");

function findLongestWord(str) {

return str.length;

}

findLongestWord("The quick brown fox jumped over the lazy dog");

We need to write the code inside the findLongestWord function that will return the length of the longest word. FCC then starts to check your code by calling findLongestWord with the string ‘The quick brown fox jumped over the lazy dog’.

We can start by splitting the original string into an array of individual words as such:

  var wordArray = str.split(" ");

1	var wordArray = str.split(" ");

We also need to create a variable to store the value representing the length of the longest word.

  var wordLength = 0;

1	var wordLength = 0;

Now we need to write a loop to go through wordArray and look for the longest word. Something to help with both these tasks is the method .length which can be used on both strings and arrays. String.length will return the number of characters in a string. Array.length will return the number of elements in an array.

A for loop is an easy way to iterate through an array. The for loop is different from the while loop used in the last algorithm in that it is initiated using three statements. A decent intro to a for loop can be found here but I’ll try to use an example to illustrate how it works:

for (var i = 0; i < 5; i++){
//code here iterates 5 times
}

for (var i = 0; i < 5; i++){

//code here iterates 5 times

}

The first statement (var i = 0;) executes before the loop begins. In this case, we initialize a variable (i) to equal 0. The second statement (i < 5) is the condition that must remain true for the loop to continue. In this case, the loop will iterate 5 times (while i is equal to 0 through 4). The third statement is executed at the end of each iteration, in this case, i is incremented by 1 each time.

Combining everything we’ve discussed thus far to solve the algorithm:

function findLongestWord(str) {
  //split str into an array of words
  var wordArray = str.split(" ");
  //create var to hold length of longest word
  var wordLength = 0;
  //loop through each word in wordArray
  //if the length of the word is longer than previous longest word
  //store new longest word in wordLenght
  for (var i = 0; i < wordArray.length; i++){
    if (wordArray[i].length > wordLength){
      wordLength = wordArray[i].length;
    }
  }
  return wordLength;
}

function findLongestWord(str) {

//split str into an array of words

var wordArray = str.split(" ");

//create var to hold length of longest word

var wordLength = 0;

//loop through each word in wordArray

//if the length of the word is longer than previous longest word

//store new longest word in wordLenght

for (var i = 0; i < wordArray.length; i++){

if (wordArray[i].length > wordLength){

wordLength = wordArray[i].length;

}

return wordLength;

}

The comments in the code ( everything following //) should help you follow the logic. The only thing in the code that we didn’t cover previously is the if statement. The code is fairly self explanatory, but you can read up on if statements on this MDN page. Basically, if the statement inside the () of an if statement is true, the code following (either a single line or a block inside {}) is executed. In this function, the if statement is used to check if the current word is longer than the previous longest word. If true, the length of the new longest word is stored in wordLength.

Hopefully this straightened out the code for you. See you next time.

-Jeremy

FCC ‘Factorialize a Number’

freeCodeCamp’s Basic Algorithm Scripting section – ‘Factorialize a Number‘

We’ll start digging into the freeCodeCamp (FCC) curriculum with ‘Factorialize a number’ because it’s pretty straight forward and it’ll allow us to discuss the structure of functions and introduce loops (This problem can also be solved with recursion, but we’ll get into that with some of the more complex algorithms).

The challenge is to write a function that will return the factorial of the number provided.

To understand factorials better, feel free to check out wikipedia, but basically, a factorial is the product of all integers less than or equal to n and is expressed as n! (i.e. 4! = 4 x 3 x 2 x 1 = 24).

FCC provides the following starting point:

function factorialize(num) {
return num;
}

factorialize(5);

function factorialize(num) {

return num;

}

factorialize(5);

As I mentioned in my first post, a function is a block of code that acts independently to perform a task. It can be called from other parts of your program, and therefore, can be used over and over to perform the same ‘function’. Functions have many uses in JavaScript, check out Eloquent JavaScript – chapter 3 to learn more.

As you can see above, the function we’ll be building is named factorialize and has one parameter (num). The way it’s written above, it returns that parameter (the body of a function is contained in {}). The function is then called on line 5 and passed the argument (5).

We need to add the code that will take the parameter (num) and calculate and return the factorial of ‘num’.

We’ll start by declaring a variable to store the value of the factorial and set it equal to 1.

var total = 1;

1	var total = 1;

We’ll add the code to calculate the factorial using a while loop. Loops allow us to set a condition, then execute a block of code until that condition is met. MDN gives a pretty good intro to while loops here.

We’ll use the argument (num) in our condition and say:

while(num>1){
}

1 2	while(num>1){ }

This while loop will now iterate until num>1 is false. Therefore, we have to remember to somehow change num each time so that eventually the loop will end (otherwise, we have an infinite loop and the program will never complete).

Now we have to do something each time the loop iterates, this is where our variable total comes in. Given that JavaScript will execute the right side of an equation before it stores it to the left side, we can set total = total * num, then depricate num by 1. That would look something like this:

  while (num > 1) {
    total = total * num;
    num = num -1;
  }

while (num > 1) {

total = total * num;

num = num -1;

}

If we walk through this for num = 5, the first pass would be

total = 1 * 5;
num = 5 -1;

1 2	total = 1 * 5; num = 5 -1;

Now total = 5 and num = 4. Since 4 > 1, the while loop will execute again.

total = 5 * 4;
num = 4 - 1;

1 2	total = 5 * 4; num = 4 - 1;

Now total = 20 and num = 3. This will continue until the while (num>1) fails. It would look like this.

total = 20 * 3;
num = 3 - 1;

1 2	total = 20 * 3; num = 3 - 1;

total = 60, num = 2.

total = 60 * 2;
num = 2 - 1;

1 2	total = 60 * 2; num = 2 - 1;

total = 120, num = 1.

At this point, the while loop condition would be false, and the loop would end with total = 120. Given 5! = 120, we have the right total, we just need to return it. We can just change the return statement from return num; to return total;.

Putting everything together:

function factorialize(num) {
  var total = 1;
  while (num > 1) {
    total = total * num;
    num = num -1;
  }
  return total;
}

function factorialize(num) {

var total = 1;

while (num > 1) {

total = total * num;

num = num -1;

}

return total;

}

This gives us the correct answer, but JavaScript makes statements that add, subtract, multiply or divide a number by itself much easier to write using the following operators: +=, -=, *= and /=. You can also increment and deprecate by 1 using ++ and — respectively. See the w3schools page on operators for more info. Knowing that, the solution seen above can be written:

function factorialize(num) {
  var total = 1;
  while (num > 1) {
    total *= num;
    num--;
  }
  return total;
}

function factorialize(num) {

var total = 1;

while (num > 1) {

total *= num;

num--;

}

return total;

}

These two solutions do the exact same thing and solve the ‘Factorialize a Number’ algorithm challenge.

Hopefully this straightened out the code for you. See you next time.

-Jeremy