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FCC Algorithm Challenges / Return Largest Numbers in Arrays

virenb profile image Viren B Updated on ・3 min read

Solving freeCodeCamp's Algorithm Challenges (37 Part Series)

1) FCC Algorithm Challenges / Convert Celsius to Fahrenheit 2) FCC Algorithm Challenges / Reverse a String 3 ... 35 3) FCC Algorithm Challenges / Factorialize a Number 4) FCC Algorithm Challenges / Find the Longest Word in a String 5) FCC Algorithm Challenges / Return Largest Numbers in Arrays 6) Solving "Confirm the Ending" / FreeCodeCamp Algorithm Challenges 7) Solving "Repeat a String Repeat a String" / FreeCodeCamp Algorithm Challenges 8) Solving "Truncate a String" / freeCodeCamp Algorithm Challenges 9) Solving "Finders Keepers" / freeCodeCamp Algorithm Challenges 10) Solving "Boo who" / freeCodeCamp Algorithm Challenges 11) Solving "Title Case a Sentence" / freeCodeCamp Algorithm Challenges 12) Solving "Slice and Splice" / freeCodeCamp Algorithm Challenges 13) Solving "Falsy Bouncer" / freeCodeCamp Algorithm Challenges 14) Solving "Where do I Belong" / freeCodeCamp Algorithm Challenges 15) Solving "Mutations" / freeCodeCamp Algorithm Challenges 16) Solving "Chunky Monkey" / freeCodeCamp Algorithm Challenges 17) Solving "Sum All Numbers in a Range" / freeCodeCamp Algorithm Challenges 18) Solving "Diff Two Arrays" / freeCodeCamp Algorithm Challenges 19) Solving "Seek and Destroy" / freeCodeCamp Algorithm Challenges 20) Solving "Wherefore art thou" / freeCodeCamp Algorithm Challenges 21) Solving "Spinal Tap Case" / freeCodeCamp Algorithm Challenges 22) Solving "Pig Latin" / freeCodeCamp Algorithm Challenges 23) Solving "Search and Replace" / freeCodeCamp Algorithm Challenges 24) Solving "DNA Pairing" / freeCodeCamp Algorithm Challenges 25) Solving "Missing letters" / freeCodeCamp Algorithm Challenges 26) Solving "Sorted Union" / freeCodeCamp Algorithm Challenges 27) Solving "Convert HTML Entities" / freeCodeCamp Algorithm Challenges 28) Solving "Sum All Odd Fibonacci Numbers" / freeCodeCamp Algorithm Challenges 29) Solving "Sum All Primes" / freeCodeCamp Algorithm Challenges 30) Solving "Smallest Common Multiple" / freeCodeCamp Algorithm Challenges 31) Solving "Drop it" / freeCodeCamp Algorithm Challenges 32) Solving "Steamroller" / freeCodeCamp Algorithm Challenges 33) Solving "Binary Agents" / freeCodeCamp Algorithm Challenges 34) Solving "Everything Be True" / freeCodeCamp Algorithm Challenges 35) Solving "Arguments Optional" / freeCodeCamp Algorithm Challenges 36) Solving "Make a Person" / freeCodeCamp Algorithm Challenges 37) Solving "Map the Debris" / freeCodeCamp Algorithm Challenges

Original post can also be found on my website, https://virenb.cc/fcc-005-largest-numbers

Return Largest Numbers in Array

function largestOfFour(arr) {
  return arr;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);



/// TESTS
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]) should return an array.
largestOfFour([[13, 27, 18, 26], [4, 5, 1, 3], [32, 35, 37, 39], [1000, 1001, 857, 1]]) should return [27, 5, 39, 1001].
largestOfFour([[4, 9, 1, 3], [13, 35, 18, 26], [32, 35, 97, 39], [1000000, 1001, 857, 1]]) should return [9, 35, 97, 1000000].
largestOfFour([[17, 23, 25, 12], [25, 7, 34, 48], [4, -10, 18, 21], [-72, -3, -17, -10]]) should return [25, 48, 21, -3]

Above is the starter code provided for the challenge, "Return Largest Numbers in Arrays."

Our goal is to write a function that to take the input of a 2D array and return the largest number of each sub-array. The output format is to be an array. There are a few ways to iterate through an array. Let's think about this.

Thoughts

  • We are dealing with a 2-Dimensional array, meaning we will have to access values from an array within an array
  • Is the way to use two for loops?
  • Having some familiarity with arrays, we have some built in methods we can resort to
  • Since we have to take the largest number from each sub array, it would be helpful if the arrays were sorted from biggest to smallest
  • There is an array method, sort(), which would be helpful. There is a link below which shows how it is to be used. We need to provide a function to compare as sort's argument sort((a, b) => b - a)
  • Since our sub-array will be sorted in largest to smallest order, we can just do one loop and push the first index of each sub-array into the newArr empty array which was declared in the function already
  • Make sure to return newArr

Solution

Some Pseudocode

function largestOfFour(arr) {
  declare new empty array   

 loop through arr item (so arr.length)
    sort each sub array (so its in order from largest to smallest)  push first index (now largest) into new array (declared above)

 return new array
}

[SPOILER: SOLUTION TO CODE BELOW]

function largestOfFour(arr) {
  let newArr = [];

  for (let i = 0; i < arr.length; i++) {
    arr[i].sort((a, b) => b - a);
    newArr.push(arr[i][0]);
  };

  return newArr;
}

Method

  1. Read (!)

    • Read the instructions first. Make sure you understand what it being asked of you.
    • Read the starter code. Go line by line, just making sure you know what is going on initially.
    • Have a look at the tests. If the problem isn't clear to you, looking at the tests might give you an inclination of what kind of output you should aim for (i.e. instead of returning an array, maybe the problem is only asking for an index within the array).
  2. Think & Write

    Now that you've read through the instructions, starter code, and tests, it's time to analyze what to do and in what order. It may be handy to write out pseudocode.

  3. Code

    Once you've thought about what you'd like to do, and in what order, start to convert your pseudocode into JavaScript code.

There's been too many times where I've tried to jump write into writing the code without thinking it through (in projects and coding challenges). That will leave you testing it way too many times, creating unnecessary variables, and running into more problems then you need to handle. If I try to follow the above method, it leaves me with a more clear mind of what I'm doing and hopefully writing some DRY code.

Links & Resources

Return Largest Numbers in Array on FCC

FreeCodeCamp

Donate to FCC!

Solution on my GitHub

Array.prototype.sort() MDN Docs

Thank you for reading!

Solving freeCodeCamp's Algorithm Challenges (37 Part Series)

1) FCC Algorithm Challenges / Convert Celsius to Fahrenheit 2) FCC Algorithm Challenges / Reverse a String 3 ... 35 3) FCC Algorithm Challenges / Factorialize a Number 4) FCC Algorithm Challenges / Find the Longest Word in a String 5) FCC Algorithm Challenges / Return Largest Numbers in Arrays 6) Solving "Confirm the Ending" / FreeCodeCamp Algorithm Challenges 7) Solving "Repeat a String Repeat a String" / FreeCodeCamp Algorithm Challenges 8) Solving "Truncate a String" / freeCodeCamp Algorithm Challenges 9) Solving "Finders Keepers" / freeCodeCamp Algorithm Challenges 10) Solving "Boo who" / freeCodeCamp Algorithm Challenges 11) Solving "Title Case a Sentence" / freeCodeCamp Algorithm Challenges 12) Solving "Slice and Splice" / freeCodeCamp Algorithm Challenges 13) Solving "Falsy Bouncer" / freeCodeCamp Algorithm Challenges 14) Solving "Where do I Belong" / freeCodeCamp Algorithm Challenges 15) Solving "Mutations" / freeCodeCamp Algorithm Challenges 16) Solving "Chunky Monkey" / freeCodeCamp Algorithm Challenges 17) Solving "Sum All Numbers in a Range" / freeCodeCamp Algorithm Challenges 18) Solving "Diff Two Arrays" / freeCodeCamp Algorithm Challenges 19) Solving "Seek and Destroy" / freeCodeCamp Algorithm Challenges 20) Solving "Wherefore art thou" / freeCodeCamp Algorithm Challenges 21) Solving "Spinal Tap Case" / freeCodeCamp Algorithm Challenges 22) Solving "Pig Latin" / freeCodeCamp Algorithm Challenges 23) Solving "Search and Replace" / freeCodeCamp Algorithm Challenges 24) Solving "DNA Pairing" / freeCodeCamp Algorithm Challenges 25) Solving "Missing letters" / freeCodeCamp Algorithm Challenges 26) Solving "Sorted Union" / freeCodeCamp Algorithm Challenges 27) Solving "Convert HTML Entities" / freeCodeCamp Algorithm Challenges 28) Solving "Sum All Odd Fibonacci Numbers" / freeCodeCamp Algorithm Challenges 29) Solving "Sum All Primes" / freeCodeCamp Algorithm Challenges 30) Solving "Smallest Common Multiple" / freeCodeCamp Algorithm Challenges 31) Solving "Drop it" / freeCodeCamp Algorithm Challenges 32) Solving "Steamroller" / freeCodeCamp Algorithm Challenges 33) Solving "Binary Agents" / freeCodeCamp Algorithm Challenges 34) Solving "Everything Be True" / freeCodeCamp Algorithm Challenges 35) Solving "Arguments Optional" / freeCodeCamp Algorithm Challenges 36) Solving "Make a Person" / freeCodeCamp Algorithm Challenges 37) Solving "Map the Debris" / freeCodeCamp Algorithm Challenges

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Viren B

@virenb

Self-taught developer, always looking to learn more.

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