Algorithms

Javascript Algorithms

Algorithm is a set of rules to accomplish a computational task.

1. Reverse string

Problem Statement

Return a new string with the reversed order of characters.

Strategy

declare a function and give it a string as parameter
use the split method to convert the string into an array
use reverse method to reverse the items in the array
then use the join method to convert the array back into a string
return the string

Code

function reverse(str) {
    return str
    .split('')
    .reverse()
    .join('')
    return str
}

2. Palindrome

Problem Statement

Palindromes are strings that form the same word when reversed. i.e kayak, civic. Return true if the string is a palindrome or false if it is not.

Strategy

declare a function and give it a string as parameter
use the split method to covert the string into an array
use reverse method to reverse the items in the array
use the join method to convert the array back into a string
then check to see if the reversed string and original string is truthy or falsy.

Code

function palindrome(str) {
  let reversed = str.split('').reverse().join('');
    return reversed === str;
}

3. Fizzbuzz

Problem Statement

Write a script that prints the number 1 to n, however for multiples of 3 - print "fizz", for multiples of 5 - print "buzz" and finally for multiples of 3 and 5 - print "fizbuzz".

Strategy

declare a function and give it a number as parameter
write a for loop to iterate from 1 to n
write multiple else if statements
condition 1 checks if n modulo 3 and n modulo 5 equals 0 then console log 'fizzbuzz'
condition 2 checks if n modulo 3 equals 0 then console log 'fizz'
condition 3 checks if n modulo 5 equals 0 then console log 'buzz'
else console log any number outside of the aforementioned conditions

Code

function fizzBuzz(n) {
  for (let i = 1; i <= n; i++) {
    if (i % 3 === 0 && i % 5 === 0) {
      console.log('fizzbuzz');
    } else if (i % 3 === 0) {
      console.log('fizz');
    } else if (i % 5 === 0) {
      console.log('buzz');
    } else {
      console.log(i);
    }
  }
}

4. Reverse Integer

Problem Statement

Given an integer, return an integer that is reversed while satisfying the following conditions i.e 15 returns 51, -25 returns -52, 100 returns 1.

Strategy

declare a function and give it a number as parameter
use the toString method to covert the integer into an string
use reverse method to reverse the string
use the join method to join the string
use the parseInt method to convert the string back to an integer
then use the Math.sign method to maintain negative numbers

Code

function reverseInt(n) {
  const reverse = n
    .toString()
    .split('')
    .reverse()
    .join('')
return parseInt(reverse) * Math.sign(n)
}

Alternative

function reverseInt(n) {
  const reverse = n
  .toString()
  .split('')
  .reverse()
  .join('')
  
// use the ternary operator to check if the integer is negative
  const checkNegativeSign = n < 0 ? parseInt(reverse) * -1 : parseInt(reverse)  
  return checkNegativeSign
  }

5. Max Character

Problem Statement

Given a string, return the most repeated character that occurs in the string. i.e "apple" === 'p'

Strategy

declare a function and give it a string as parameter
using the for of loop, generate an object named 'charMap' that maps each character in the string to the object.
declare a helper variable named 'max' that stores the maximum value of the string most repeated in the object.
declare another helper variable named 'maxChar' that stores the most repeated character.
iterate through the object using a for in loop while incrementing the "max" variable and assigning the "maxChar" variable with the most repeated character.
return maxChar

Code

function maxChar(str) {
  const charMap = {}
  let max = 0
  let maxChar = ''

  for (let char of str) {
    charMap[char] ? charMap[char]++ : charMap[char] = 1
  }

  for (let char in charMap) {
    if (charMap[char] > max) {
      max = charMap[char]
      maxChar = char
    }
  }
  return maxChar
}

6. Array Chunking

Problem Statement

Given an array and chunk size, divide the array into many subarrays where each subarray is of length size. i.e [1, 2, 3, 4] --> [[1,2], [3, 4]]

Strategy

declare a function and give it an array and size as parameter
create a helper variable named chunked that stores chunks of subarrays where each array is of length size.
create another helper variable named index starting from 0
in a while loop, iterate from index up to length of array
using the slice method, push slices of subarrays that equals of length size into chunked
increment index with 'size' to kill the loop
return chunked

Code

function chunk(array, size) {
  const chunked = []
  let index = 0

  while (index < array.length) {
  chunked.push(array.slice(index, index + size))
  index += size
  }
  return chunked
}

7. Anagrams

Problem Statement

Given two strings, check to see if they anagrams of each other. An anagram is a word, phrase, or name formed by rearranging the letters of another, such as cinema, formed from iceman. Capital letter should be lowercase, no spaces or punctuations allowed. i.e "RAIL SAFETY!", "fairy tales" --> True.

Strategy

declare a function anagrams and give it two strings as parameter.
declare another helper function cleanStringthat formats the string by removing undesired characters and transforms letters to lowercase.
after formatting the string with cleanString, use the function anagrams to compare both strings to each other
return anagrams.

Code

function anagrams(stringA, stringB) {
  return cleanString(stringA) === cleanString(stringB)
}

function cleanString(str) {
  return str.replace(/[^\w]/g, '').split('').sort().join('')
}

8. Sentence Capitalization

Problem Statement

Write a function that capitalizes the first letter of each word. i.e "i love javascript" --> "I Love Javascript"

Strategy

declare a function capitalize and give it a string as parameter.
make an empty array named words to store transformed words
iterate over the array while using split to convert each string into an array
apply toUpperCase to transform the first character in each word then concatenate the remaining characters using the slice method
push the transformed words into the empty array named words.
join array back into string and return.

Code

function capitalize(str) {
  const words = []

  for (let word of str.split(' ')) {
    words.push(word[0].toUpperCase() + word.slice(1)) 
  }
  return words.join(' ')
}

9. Stairsteps

Problem Statement

Write a function that takes a positive number and prints a step shape N levels using the "#" character. i.e stairSteps(3) should return -->

'# '

'## '

'###'

consider the trailng empty spaces within quotes

Strategy

declare a function steps and give it a positive number as parameter.
create a 3 x 3 matrix by iterating from 0 to n for (i) rows and (j)columns
if column is less than or equal to row, increment stair with '#'
else increment steps with ' '
console.log(steps)

Code

function stairSteps(n) {
  for (row = 0; row < n; row++) {
    let steps = ''

    for(column = 0; column < n; column++) {
      if (column <= row) {
        steps += '#'
      }
      else {
        steps += ' '
      }

    }
    console.log(steps);
  }
}

10. Pyramid

Problem Statement

Write a function that accepts a positive number N. The function should output a pyramid shape with N levels using the # character. Make sure the pyramid has spaces on both the left and right hand sides. i.e pyramid(3) -->

' # '

' ### '

'#####'

Strategy

declare a function pyramid and give it a positive number as parameter.
write a for loop that iterates through each n rows.
create a variable 'level' that assigns empty space to each row.
write another for loop that iterates over columns such that when given n, each column computes logic that doubles n and subtracts 1.
in order to assign "#" to the matrix created, create a variable midpoint that locates index of the row's midpoint.
use a if block to assign # when midpoint minus row is less than and equal to column and when midpoint plus row greater than and equal to column else add an empty space
return level

Code

function pyramid(n){
  const midpoint = Math.floor((2 * n - 1)/2)

  for (let row = 0; row < n; row++) {
    let level = ''

    for (let column = 0; column < 2 * n - 1; column++){
      if (midpoint - row <= column && midpoint + row >= column){
        level += '#'
      } else {
        level += ' '
      }

    }
    console.log(level);
  }
}

11. Vowels

Problem Statement

Write a function that returns the number of vowels used in a string. Vowels are the characters 'a', 'e''i', 'o', and 'u'. i.e. vowels('Hi There!') --> 3

Strategy

declare a function vowels and give it string as parameter.
assign 0 to a variable labeled counter to count occurences of a vowel
assign characters in vowels to a variable labeled `vowels'
iterate through lowercased characters in given string and check if it includes any vowels
if so, increment counter
return counter

Code

function vowels (str) {
  let counter = 0
  const vowels = ['a', 'e', 'i', 'o', 'u']
  
  for (let char of str.toLowerCase()) {
    if (vowels.includes(char)) {
      counter++
    } 
  }
  return counter
}

12. Factorialize

Problem Statement

Write a function that returns the factorial of the provided integer for example:

5! = 1 * 2 * 3 * 4 * 5 = 120

Strategy

declare a function named factorialize and give it integer as parameter.
assign 1 to a variable named result
iterate through given integer and multiply each iteration of given argument by result
return result

Code

function factorialize(num) {
  let result = 1
  for (let i = 1;  i <= num;  i++) {
    result = result * i
  }
  return result
}

Resources:

The Coding Interview Bootcamp: Algorithms + Data Structures

Freecodecamp

MDN Javascript Guide

b-45/algorithms-javascript

Algorithms

1. Reverse string

Problem Statement

Strategy

Code

2. Palindrome

Problem Statement

Strategy

Code

3. Fizzbuzz

Problem Statement

Strategy

Code

4. Reverse Integer

Problem Statement

Strategy

Code

Alternative

5. Max Character

Problem Statement

Strategy

Code

6. Array Chunking

Problem Statement

Strategy

Code

7. Anagrams

Problem Statement

Strategy

Code

8. Sentence Capitalization

Problem Statement

Strategy

Code

9. Stairsteps

Problem Statement

Strategy

Code

10. Pyramid

Problem Statement

Strategy

Code

11. Vowels

Problem Statement

Strategy

Code

12. Factorialize

Problem Statement

Strategy

Code