Count the smiley faces! Regular Expressions?

JavaScript
1

challenge : https://www.codewars.com/kata/583203e6eb35d7980400002a
I’m wondering if anyone know how to solve this challenge with regular expressions? because in the challenge, it has a “regular expression” tag attached to it.

i passed this with my code :

//return the total number of smiling faces in the array
function countSmileys(arr) {
if ( arr.length === 0 )  { 
  return 0;
}
let incr = 0;
let validSmileys = [":)",";)",":D",";D",":-D",":~D",":-)",":~)",";~D",";~)",";-D",";-)"]
for (let face of arr) { 
  if (validSmileys.includes(face)) { 
    incr++;
  }
}
return incr;
}

countSmileys([";~D" , ":o>" , ";~)" , ":)" , ";~>" , ":(" , ";D"])


// : or ;
// - or ~
// ) or D.
2

you need a pattern that is tiny bit complex and the test method, so it return true/false if it matches or not

remember that you create a class of characters using square parenthesis,
so if you write [abc] it matches any of the letters inside it

1 Like
3

@Gerwyn Solving with a regular expression is fairly simple.

function countSmileys(arr) {
  const matches = arr.join('').match(/[:;][-~]?[D)]/g);
  return matches ? matches.length : 0;
}

However, if you are not using the regular expression, I think instead of using the array as the lookup, it would be faster to use an object lookup.

function countSmileys(arr) { 
  const validSmileys = {
    ":)": true, ";)": true, ":D": true,
    ";D": true, ":-D": true, ":~D": true,
    ":-)": true, ":~)": true, ";~D": true,
    ";~)": true, ";-D": true, ";-)": true
  };
  return arr.filter(chars => validSmileys[chars]).length;  
}
2 Likes
4

I learned regex but its a bit cloudy for me since i don’t use it much. your example reinforced the practicality of them for me. as for the OOP example, i tried and they worked but im wondering though, shouldn’t they return an array of true values? like [true,true…] since validSmileys[chars] gives the value of the property which is true. that’s the only thing im confused of really.

5

I used test method instead of match and it works fine too.

function countSmileys(arr) {

let faceRegex= /[;:][~-]?[)D]/
let incr = 0;
for (face of arr) { 
  if (faceRegex.test(face)) { 
    incr++;
  }
}
return incr;
}

countSmileys([':)',':(',':D',':O',':;'])
6

I always have to refer to the MDN documentation of RegEx. Very helpful.

7

i prefer w3schools tbh. it just shows a practical example immediately

1 Like
9

right so it only filters the ones in the array. and the ones that only are filtered are the ones who had return true?