Jika Anda mencari tutorial mempelajari Javascript benar-benar dari awal, dan memang fokus pada implementasi bahasanya, maka seri ini adalah jawabannya.

Problem Solving

Duplicate Encoder


> Problem

The goal of this exercise is to convert a string to a new string where each character in the new string is "(" if that character appears only once in the original string, or ")" if that character appears more than once in the original string. Ignore capitalization when determining if a character is a duplicate.

### Example:

```tsx
"din"      =>  "((("
"recede"   =>  "()()()"
"Success"  =>  ")())())"
"(( @"     =>  "))(("
```

### Notes:

Assertion messages may be unclear about what they display in some languages. If you read "...It Should encode XXX", the "XXX" is the expected result, not the input!

&nbsp;

> Solution

The goal of this problem is to convert a given string into a new string based on the following rules:

1. Each character in the new string will be replaced with "(" if that character appears only once in the original string.
2. If a character appears more than once in the original string, it will be replaced with ")" in the new string.

Here are some important points to consider:

- Capitalization differences should be ignored. This means that uppercase and lowercase letters are considered the same. So, "A" and "a" are treated as the same character.
- Spaces or non-alphabetic characters should be ignored in the counting. Only alphabetic characters are considered.

For example, if we have the original string "recede", the resulting string will be "()()()". This is because the characters "r" and "d" appear only once, while the character "e" appears three times.

Here are a few more examples of string conversions:

- Original string: "din", converted string: "(((" because all characters ("d", "i", and "n") appear only once.
- Original string: "recede", converted string: "()()()" because the character "e" appears three times, while the other characters appear only once.
- Original string: "Success", converted string: ")())())" because the character "s" appears three times, the character "c" appears twice, and the other characters appear only once.
- Original string: "(( @", converted string: "))((" because the character "(" appears twice, while the other characters appear only once.

## Step-by-step Explanation

Here are the steps in solving the "Duplicate Encoder" problem using JavaScript:

1. Start by defining a function called **`duplicateEncode`** that takes a single parameter, **`word`**. This function will be used to convert the input string according to the given rules.
2. Inside the **`duplicateEncode`** function, convert the **`word`** to lowercase using the **`.toLowerCase()`** method. Save the result in a variable called **`lowercaseWord`**. This is done to ignore capitalization differences.
3. Create an empty variable called **`result`** to store the converted string.
4. Begin iterating through each character in the **`lowercaseWord`** string. For each character, follow these steps:
   - Take the character at index **`i`** using **`lowercaseWord[i]`** and store it in a variable called **`char`**.
   - Count the number of occurrences of the **`char`** in **`lowercaseWord`** by splitting the string into an array using the **`.split()`** method and then obtaining the length of the resulting array using the **`.length`** property. Subtract 1 from the length because the split method will create an array with one extra element.
   - If the count is greater than 1, it means the character is a duplicate. In this case, add ")" to the **`result`** variable.
   - If the count is equal to 1, it means the character appears only once. In this case, add "(" to the **`result`** variable.
5. After iterating through all the characters in **`lowercaseWord`**, return the value of the **`result`** variable as the converted string.
6. Finally, you can call the **`duplicateEncode`** function by providing the input string that you want to convert and store the result in a variable for further use or print it to the console.

Here's the complete implementation in JavaScript:

```tsx
function duplicateEncode(word) {
  const lowercaseWord = word.toLowerCase();
  let result = '';

  for (let i = 0; i < lowercaseWord.length; i++) {
    const char = lowercaseWord[i];
    const count = lowercaseWord.split(char).length - 1;

    if (count > 1) {
      result += ')';
    } else {
      result += '(';
    }
  }

  return result;
}

// Usage example:
const input = 'Success';
const encodedString = duplicateEncode(input);
console.log(encodedString);
```

The resulting output will be printed to the console:

```tsx
)())())
```

In this example, the string "Success" is converted to ")())())" according to the rules given in the problem.


Sentence Smash


> Problem

Write a function that takes an array of words and smashes them together into a sentence and returns the sentence. You can ignore any need to sanitize words or add punctuation, but you should add spaces between each word. Be careful, there shouldn't be a space at the beginning or the end of the sentence!

### Example :

```
['hello', 'world', 'this', 'is', 'great']  =>  'hello world this is great'
```

&nbsp;

> Solution

```
function smash(words) {
  var sentence = words.join(' '); // Join the words with a space in between
  return sentence;
}

var words = ['hello', 'world', 'this', 'is', 'great'];
var result = smash(words);
console.log(result);
```

Let me explain how the code works:

1.  We define a function called smash that takes an array of words as its parameter.
2.  Inside the function, we use the join method on the words array. The join method concatenates all the elements of an array into a single string, with the specified separator in between. In this case, we use a space ‘ ‘ as the separator.
3.  The resulting string is stored in the variable sentence.
4.  Finally, we return the sentence from the function.
5.  Outside the function, we create an array called words with the given words.
6.  We call the smash function with the words array as an argument and store the result in the variable result.
7.  Finally, we log the result to the console, which will display the sentence.

When you run this code, the output will be:

```
hello world this is great
```

So, the function joins all the words in the array together with spaces and returns the resulting sentence.


Count by X


> Problem

Create a function with two arguments that will return an array of the first n multiples of x.

Assume both the given number and the number of times to count will be positive numbers greater than 0.

Return the results as an array or list ( depending on language ).

Examples

```
countBy(1,10) === [1,2,3,4,5,6,7,8,9,10]
countBy(2,5) === [2,4,6,8,10]
```

&nbsp;

> Solution

```
const countBy = (x, n) => {
    let result = []

    for(let i = 1; i <= n; i++) {
        result.push(x * i)
    }

    return result
}
```

In this JavaScript implementation, we initialize an empty array result. Then, we use a for loop to iterate from 1 to n (inclusive). Inside the loop, we multiply x by the current iteration i and push the result into the result array using the push method. Finally, we return the result array.

For example, `countBy(1, 10)` would return `[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]`, and `countBy(2, 5)` would return `[2, 4, 6, 8, 10]`.


Even or Odd


> Problem

Create a function that takes an integer as an argument and returns "Even" for even numbers or "Odd" for odd numbers.

&nbsp;

> Solution

JavaScript Function to Check Even or Odd:

```
function even_or_odd(number) {
  // Step 1: Check if the number is even or odd
  if (number % 2 === 0) {
    // Step 2: If the number is even, return "Even"
    return "Even";
  } else {
    // Step 3: If the number is odd, return "Odd"
    return "Odd";
  }
}

```

Explanation:

We define a function called even_or_odd that takes a single parameter called number, which represents the integer we want to check.

Inside the function, we use the modulus operator % to check if the number is even or odd. The modulus operator returns the remainder of a division operation. If a number is even, it will be perfectly divisible by 2, so its remainder when divided by 2 will be 0. If it's odd, the remainder will be 1.

We check if number % 2 === 0. If the condition is true (the number is even), we execute the code inside the if block, which returns the string "Even".

If the condition in Step 3 is false (the number is odd), we execute the code inside the else block, which returns the string "Odd".

Examples:

Let's call the function with some examples to see how it works:

```
console.log(even_or_odd(5));  // Output: "Odd"
console.log(even_or_odd(10)); // Output: "Even"
console.log(even_or_odd(0));  // Output: "Even"
console.log(even_or_odd(-3)); // Output: "Odd"
```

In the first example, we pass the number 5 to the function, and it returns "Odd" because 5 is an odd number.

In the second example, we pass the number 10, which is even, so the function returns "Even".

In the third example, we pass 0, which is also an even number, so the function returns "Even".

In the last example, we pass -3, which is an odd number, and the function returns "Odd". The function works correctly for negative integers as well.

Hope this helps!


Sum without highest and lowest number


> Problem

Sum all the numbers of a given array ( cq. list ), except the highest and the lowest element ( by value, not by index! ).

The highest or lowest element respectively is a single element at each edge, even if there are more than one with the same value.

Mind the input validation.

Example

```
{ 6, 2, 1, 8, 10 } => 16
{ 1, 1, 11, 2, 3 } => 6
```

Input validation

If an empty value ( null, None, Nothing etc. ) is given instead of an array, or the given array is an empty list or a list with only 1 element, return 0.

&nbsp;

> Solution

To solve this problem in JavaScript, we'll follow these steps:

1.  Input validation: The function starts by checking for input validation. If the input is not an array or the array has less than two elements (meaning it has only one element or it's empty), the function returns 0. This step ensures that the function is dealing with valid input.

2.  Sorting the array: The array.sort((a, b) => a - b) part sorts the input array in ascending order. This step is necessary to ensure that the lowest and highest elements are at the beginning and end of the array, respectively.

3.  Slicing the array: The slice(1, -1) part removes the first and last elements from the sorted array. Since the array is now sorted, these elements correspond to the lowest and highest values.

4.  Summation: The reduce((a, b) => a + b, 0) part calculates the sum of the remaining elements in the array. It uses the reduce method to iterate through the array and accumulate the sum.

5.  Returning the result: The function returns the calculated sum as the final result.
    Let's implement the solution:

```
function sumArray(array) {
  if (!array || array.length < 2) {
    return 0
  }

  const result = array.sort((a, b) => a - b).slice(1, -1).reduce((a, b) => a + b, 0)
  return result

}

// Test cases
sumArray([6, 2, 1, 8, 10]);
```

### Let's break down the code step by step:

1. Input validation:

```
if (!array || array.length < 2) {
  return 0;
}
```

This code checks the input array to see if it exists and has at least two elements. If the input array is null, undefined, or has less than two elements, the function immediately returns 0. This step is essential to handle invalid inputs and prevent errors when trying to access elements in an empty array.

2.  Sorting the array:

```
const result = array.sort((a, b) => a - b)
```

This line sorts the input array in ascending order using the `sort()` method. The provided comparison `function (a, b) => a - b` ensures that the array is sorted numerically. Sorting is necessary to identify the lowest and highest elements at the edges of the array.

Note: It's important to mention that this step modifies the original array. If you want to avoid modifying the original array, you can create a copy of the array before sorting.

3.  Slicing the array:

```
.slice(1, -1)
```

This part of the code uses the `slice()` method to extract a portion of the sorted array. The `slice()` method returns a new array that includes elements starting from the index 1 (the second element) up to, but not including, the index -1 (the last element). Essentially, it removes the first and last elements from the sorted array, which correspond to the lowest and highest values, respectively.

4.  Summation:

```
.reduce((a, b) => a + b, 0)
```

The `.reduce()` method is used to calculate the sum of the remaining elements in the array. It iterates through the sliced array, applying the provided `function (a, b) => a + b` to each element. The function accumulates the sum by adding each element b to the accumulated sum a. The initial value of the accumulator is 0, which means the summation starts from 0.

Returning the result:

```
return result;
```

Finally, the function returns the calculated sum (stored in the variable result) as the final output.

Example:
Let's illustrate the process with an example:

```
sumArray([6, 2, 1, 8, 10]);
```

- Input validation: The input array [6, 2, 1, 8, 10] has five elements, so it meets the requirements.
- Sorting the array: The sorted array is [1, 2, 6, 8, 10].
- Slicing the array: The sliced array is [2, 6, 8], excluding the lowest (1) and highest (10) elements.
- Summation: The sum of the remaining elements [2, 6, 8] is 2 + 6 + 8 = 16.
- Returning the result: The function returns 16.


Grasshopper - Personalized Message


> Problem

Create a function that gives a personalized greeting. This function takes two parameters: name and owner.

Use conditionals to return the proper message:

| Case              | Return        |
| ----------------- | ------------- |
| name equals owner | 'Hello boss'  |
| otherwise         | 'Hello guest' |

&nbsp;

> Solution

Create a function that generates a personalized greeting. This function takes two parameters: name and owner.

Use conditionals to return the proper message:

If name equals owner, return 'Hello boss'.
Otherwise, return 'Hello guest'.

```javascript
function greet(name, owner) {
  return name === owner ? 'Hello boss' : 'Hello guest';
}
```

In this solution, the greet function uses a ternary conditional operator to check whether name === owner. If they are equal, the function returns 'Hello boss'; otherwise, it returns 'Hello guest'.
