DEV Community

Coding Puzzles: Week of 4/8

Ali Spittel on April 08, 2019

I'm bringing back the coding puzzles after a few month hiatus! Every day, I post coding puzzles. These are quick coding challenges that increase i...

Read full post

Ali Spittel • Apr 9 '19

Tuesday (7 KYU): Find the stray number

codewars.com/kata/57f609022f4d534f...

Laurie • Apr 9 '19

function stray(arr) {
    return arr.reduce((a, b) => a ^ b)
}

russ • Apr 9 '19

What is this necromancy?

Laurie • Apr 9 '19 • Edited

Haha, bitwise xor. Since it's immutable and commutative it'll reduce down to the stray!

I should add that this only works because it’s an odd number of elements in the array. An even number of matching elements cancel each other out to result in the “stray”.

russ • Apr 9 '19

Oh my, it even works in python!

def stray(arr):
    count = {}
    for index, i in enumerate(arr):
        count[i] = count.setdefault(i, 0) + 1
        if index >= 2 and len(count.keys()) > 1:
            break
    return next(k for k, v in count.items() if v == 1)

from functools import reduce

def intstray(arr: [int]):
    return reduce(lambda x,y: x ^ y, arr)

assert(intstray([1, 1, 2]) == 2)
#nope..!
#assert(intstray([1, 1, 2, 1]) == 2)
assert(intstray([17, 17, 3, 17, 17, 17, 17]) == 3)
assert(intstray([1, 2, 2]) == 1)
assert(stray(["bob", "bob", "bob", "steve", "bob"]) == "steve")

Laurie • Apr 9 '19

This is one of those moments when I wish gifs worked better on Dev. But yay!

Ali Spittel • Apr 10 '19

Wednesday (6 KYU): Implement Syntax Highlighting

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

russ • Apr 11 '19 • Edited

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])

russ • Apr 13 '19

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)

Laurie • Apr 12 '19

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

Laurie • Apr 10 '19 • Edited

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 • Apr 12 '19 • Edited

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;
      }
  })
}

Ali Spittel • Apr 8 '19

Monday (8KYU): How many stairs will Suzuki climb in 20 years?

codewars.com/kata/56fc55cd1f5a93d6...

Laurie • Apr 8 '19 • Edited

Javascript (ES6):

function stairs_in_20(stairs) {
       return stairs.reduce((steps, day) => steps.concat(day)).reduce((sum, count) => sum + count) * 20;
}

Jelle Bekker • Apr 8 '19

Not a one liner like you guys but C#:

using System;
public class Kata
{
  public static long StairsIn20(int[][] stairs)
  {
    long sum = 0;
    foreach (var weekday in stairs)
        foreach (var steps in weekday)
          sum += steps;

    return sum * 20;
   }           
}

Jelle Bekker • Apr 9 '19

Okay, I couldn't help myself:

using System;
using System.Linq;

public class Kata
{
  public static long StairsIn20(int[][] stairs)
  {
    return stairs.SelectMany(x => x).Sum() * 20;
  }
}

Md Imrul Hassan • Apr 10 '19

def stairs_in_20(stairs):
    return 20*sum(sum(stairs, []))

Ali Spittel • Apr 8 '19 • Edited

My Python solution:

def stairs_in_20(stairs):
      return sum(i for sublist in stairs for i in sublist)  * 20

Ali Spittel • Apr 12 '19

Friday (CodeJam): Foregone Solution

codingcompetitions.withgoogle.com/...

Ali Spittel • Apr 12 '19

n_cases = int(input())
for i in range(1, n_cases + 1):
    check_amount = int(input())
    unfound = True
    fours = [int(i) for i in str(check_amount)]
    others = ["1" if n == 4 else "0" for n in fours]
    n = int(''.join(others))
    print("Case #{}: {} {}".format(i, n, check_amount - n))

Courtney • Apr 14 '19

brute force for me so far.

const readline = require('readline');

function foregone() {
    let argumentsArray = [], answerArray = [];
    let linecounter = 0, tests;

    const rl = readline.createInterface({ 
        input: process.stdin,
        output: process.stdout
    });
    rl.on('line', (line) => {
        linecounter++;
        if(linecounter === 1) tests = line;
        else {
            argumentsArray.push(line);
            if(linecounter > tests) rl.close();
        }
    }).on('close', () => {
        for(let i=0; i< argumentsArray.length; i++) {
            answerArray.push(noFours(argumentsArray[i]));
        }
        for(let i=0; i<answerArray.length; i++) {
            console.log(`Case #${i+1}: ${answerArray[i][0]} ${answerArray[i][1]}`)
        }
        process.exit(0);
    });

    function noFours(num) {
        let a = num - 1, b = num - a;
        while(a.toString().indexOf('4') !== -1 || b.toString().indexOf('4') !== -1 && a >= b) {
            a--, b++;
        }
        if(a.toString().indexOf('4') === -1 && b.toString().indexOf('4') === -1) return [a, b];
        else return undefined 
    }
}

E. Choroba • Apr 12 '19

#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use Math::BigInt;

chomp( my $cases = <> );
for my $case (1 .. $cases) {
    chomp( my $n = <> );
    (my $i = $n) =~ tr/4/3/;
    my $j = 'Math::BigInt'->new($n) - 'Math::BigInt'->new($i);
    say "Case #$case: $i $j";
}

Jacob Evans • Apr 9 '19

const stairsIn20 =(s) => [...s].map((ele)=> ele.reduce((ag, nx)=> ag+nx))
.reduce((ag, nx)=> ag+nx) * 20

Ali Spittel • Apr 11 '19

Thursday (5 KYU): Perimeter of squares in a rectangle

codewars.com/kata/559a28007caad2ac...

E. Choroba • Apr 11 '19

#!/usr/bin/perl
use warnings;
use strict;

sub perimeters {
    my ($n) = @_;
    my @f = (1, 1);
    my $s = 0;
    for (0 .. $n) {
        $s += $f[0];
        @f = ($f[1], $f[0] + $f[1]);
    }
    return 4 * $s
}

# In a good TDD tradition, I started with these lines:
use Test::More tests => 2;
is perimeters(5), 80;
is perimeters(7), 216;

Courtney • Apr 12 '19

TypeScript. Great practice!

export class G964 {
    public static perimeter = (n) => {
      let fibArray : number[] = [0, 1, 1];
      for(let i=3; i<=n+1; i++) {
        fibArray[i] = fibArray[i-1] + fibArray[i-2];
      }
      return fibArray.reduce((a, b) => a + b) * 4;
    }
}

Jacob Evans • Apr 9 '19

const stairsIn20 =(s) => [...s].map((ele)=> ele.reduce((ag, nx)=> ag+nx)).reduce((ag, nx)=> ag+nx) * 20