Discussion on: Coding Puzzles: Week of 4/8

[Ali Spittel]

Wednesday (6 KYU): Implement Syntax Highlighting

codewars.com/kata/roboscript-numbe...

[Laurie]

Booo regex

function highlight(code) {
  return code.replace(/(\D)\1+|(\d+|\D)/g, (substr) => {
      var color;
      let testChar = substr.charAt(0); 

      if (testChar === 'F') {
          color = 'pink';
      } else if (testChar === 'L') {
          color = 'red';
      } else if (testChar === 'R') {
          color = 'green';
      } else if (!isNaN(testChar)) {
          color = 'orange';
      } else {
        return substr;
      }
      return '<span style="color: ' + color + '">' + substr + '</span>';   
  })
}

[Laurie]

Quick edit with a dictionary.

function highlight(code) {
  const colorDict = {'F': 'pink', 'L': 'red', 'R':'green'};

  return code.replace(/(\D)\1*|\d+/g, (substr) => {
      let testChar = substr.charAt(0); 

      if (testChar in colorDict) {
        return '<span style="color: ' + colorDict[testChar] + '">' + substr + '</span>';   
      } else if (!isNaN(testChar)) {
        return '<span style="color: orange">' + substr + '</span>';   
      } else {
        return substr;
      }
  })
}

[russ]

I had no idea you could use \1 in the same expression as the tagged group, never seen that before!

[Laurie]

Stackoverflow helped me with that one. I knew it was possible, but wasn't sure how. I actually started with the (.)\1* and iterated to the right regex from there.

[russ]

You should be able to simplify it a little by changing the + to a * so you don't need the second \D I think?
(\D)\1*|(\d+)

[Laurie]

Ooh, you're right. I had it that way to start and then ran into problems with a test case that had 663. It was splitting that grouping because it hit the matching case first. But when I removed the capture group generic and made it non-digit that solved that. So can revert back. Thanks :)

[russ]

import re

def highlight(cmd):
    colour_map = [
        (r'F+', 'pink'),
        (r'L+', 'red'),
        (r'R+', 'green'),
        (r'\d+', 'orange'),
        (r'()+', None),
    ]
    highlighted = []
    while(len(cmd)):
        for regex, colour in colour_map:
            match = re.match(regex, cmd)
            if match:
                idx_start, idx_end = match.span()
                highlighted.append((cmd[idx_start:idx_end], colour))
                cmd = cmd[idx_end:]
                break
        else:
            highlighted.append((cmd[0], None))
            cmd = cmd[1:]
    return ''.join(['<span style="color: {}">{}</span>'.format(colour, string) if colour else string for string, colour in highlighted])

[Laurie]

Oooh, I like this. I was thinking about a dictionary but didn't think about a dictionary with the regex as a key!

[russ]

And now with added re.sub with a callable, which I had no idea was a thing! These coding things are pretty nifty for leaning new tricks I must say!

import re

def highlight(cmd):
    colour_map = [
        (r'F+', 'pink'),
        (r'L+', 'red'),
        (r'R+', 'green'),
        (r'\d+', 'orange'),
        (r'()+', None),
    ]

    def replacer(match : re.Match):
        substr = match.group()
        colour = next((colour for regex, colour in colour_map if re.match(regex, substr)), None)
        return '<span style="color: {}">{}</span>'.format(colour, substr) if colour else substr

    return re.sub(r'(\D)\1*|(\d+)', replacer, cmd)

[Courtney]

The answers to this kata on codewars are blowing my mind.

function highlight(code) {
    let codeString = '';
    let leftPointer, currentItem;
    let colorObj = {'F': '<span style=\"color: pink\">', 'L': '<span style=\"color: red\">', 'R': '<span style=\"color: green\">'};
    for(let i=0; i<code.length; i++){
        currentItem = code[i];
        if(!isNaN(code[i])) {
            codeString += '<span style=\"color: orange\">'
            leftPointer = i;
            while(i+1 < code.length && !isNaN(code[i+1])) {
                i++;
            }
            codeString += code.slice(leftPointer, i+1) + '</span>';
        }
        else if(colorObj[currentItem]) {
            codeString += colorObj[currentItem];
            while(i+1 < code.length && currentItem === code[i+1]) {
                i++;
                codeString += currentItem;
            }
        codeString += currentItem  + '</span>';
        }
        if(currentItem === '(' || currentItem === ')') codeString += currentItem;
    }
    return codeString;
  }