JavaScript Kata #31: Is this a triangle?

By YayoDrayber | Learn To Code With Me | 12 Sep 2022

If you missed the introductory post, it's here. For a list of previously solved katas, please refer to the bottom of this page.

If this is your first time seeing my post, please note - these katas are probably randomly assigned per user so please don't go into Codewars thinking we will have exactly the same user experience, I am just posting these in the order that I got them.

Kata #31

DESCRIPTION:

Implement a function that accepts 3 integer values a, b, c. The function should return true if a triangle can be built with the sides of given length and false in any other case.

(In this case, all triangles must have surface greater than 0 to be accepted).

Starting code:

function isTriangle(a,b,c)
{
   return false;
}

My attempt that worked:

function isTriangle(a,b,c){
  if(a > 0 && b > 0 && c > 0){
      let s = (a + b + c)/2
      let x = s-a
      let y = s-b
      let z = s-c
      let sxyz = s*x*y*z
      let area = Math.sqrt(sxyz)
      if (area > 0){
       return true
       } else {
       return false
       }
    } else {
      return false
    }
}

Took a long time to arrive at a solution that works because I somehow misunderstood the problem statement. In my mind I was thinking that if all arguments passed are at least above zero, then a triangle could be built but apparently I was wrong. Apparently there is a maximum number that the longest side could be so I had to google the formula (Heron's formula which I found here) and applied it to my code. Understanding the underlying logic of the formula was crucial to come up with a much shorter code that I have though.

Rank #1 in 'Best Practice':

function isTriangle(a,b,c)
{
   return a + b > c && a + c > b && c + b > a;
}

Rank #2 with the enviable one-liner and use of Math.max():

var isTriangle = (a,b,c) => Math.max(a,b,c)<(a+b+c)/2

Thought about the approach of converting the integers into an array and sorting it but I got stuck, which rank #3 shows how it's done:

function isTriangle(a,b,c)
{
  [a, b, c] = [a, b, c].sort((x, y) => x-y);
  
  return a+b > c;
}

Rank #4:

function isTriangle(a,b,c) {
  if(a > 0 && b > 0 && c > 0) {
    if(a < b + c && b < a + c && c < a + b) {
      return true;
    }
    else {
      return false;
    }
  }
  else {
   return false;
  }
}

Rank #5:

function isTriangle(a,b,c) {
  var sides = [a, b, c].sort();
  return (sides[0] + sides[1] > sides[2]);
}

Another "D'OH!" moment for sure. Feels like I have to go back to high school and re-learn geometry. Also maybe an indication that it's a bad idea to do several challenges at once because I might not be processing the problems as well as I should. 😵

That's it for Kata #31, stay tuned for more katas to be solved!

Link to Kata #1: Square(n) Sum

Link to Kata #2: Convert a Number to a String

Link to Kata #3: DNA to RNA Conversion

Link to Kata #4: Remove First and Last Character

Link to Kata #5: MakeUpperCase

Link to Kata #6: Total amount of points

Link to Kata #7: A Needle in the Haystack

Link to Kata #8: Sum of positive

Link to Kata #9: Basic Mathematical Operations

Link to Kata #10: Beginner - Reduce but Grow

Link to Kata #11: Square Every Digit