Code Golf tips of ruby

Code golf tips of ruby.

Remove whitespace.

There isn't need whitespace in CodeGolf.

# bad
puts "hello world"

# good
puts"hello world"

Remove parentheses

There isn't need parentheses in CodeGolf.

# bad
puts("hello")
[1,2,3].map(&:to_s)

# good
puts"hello"
[1,2,3].map &:to_s

Variable

Variables should be defined with one character.

define

# bad
word='ruby'

# good
w='ruby'

---

if same value, variables can be declared together.

# bad
a=3
b=3

# good
a=b=3

Multiple assignment

a,b,c=[1,2,3]      #=> a=1, b=2, c=3
a,b,*c=[1,2,3,4,5] #=> a=1, b=2, c=[3,4,5]
a,*b,c=[1,2,3,4,5] #=> a=1, b=[2,3,4], c=5
a,*b=1             #=> a=1, b=[]

Global variable

if $ is placed at the beginning of a variable name, it becomes a global variable.

Calling undefined global variables will only return nil and no error will occur.

$a #=> nil

Get nil with one character

p method return nil if doesn't output anything.

p p #=> nil

Use shorter method name

use methods which name shorter in code golf.

# bad
[1,2,3].find_index(2) #=> 1

# good
[1,2,3].index(2) #=> 1

Block use {...} instead of do end

# bad
10.times do|n|puts"#{n} hello"end

# good
10.times{|n|puts"#{n} hello"}

Reduce newline codes

In the Windows environment, because the newline code is defined with \r\n, reduce the number of lines.

# bad
puts'hello'
puts'world'

# good
puts'hello';puts'world'

Read the document

TBD

Comparison operator is one character

replace comparison operators ==, <= and >= with > or < if possible.

# bad
n<=3

# good
n<4

There are patterns that are shortened by using ...

# bad
(0..n-1).each{|n|p n}

# good
(0...n).each{|n|p n}

Treat logical operators as conditional expressions

Use short-circuit evaluation and treat logical operators && and || as conditional expressions.

# bad
if true
  n=3
end

# good
true&&n=3

# bad
unless false
  n=3
end

# good
false||n=3

Ternary operator

# bad
if 3>2
  333
else
  777
end

# good
3>2?333:777

Special

# bad
a=[] #=> []

# good
$* #=> []

---

# bad
ARGV

# good
$*

---

# bad
"\n"

# good
$/

Command Line Option

It is important to shorten a processing of input.

bad

while gets
  puts $_
end

Add option 「-n」, each input line is inserted into variable $_.

good

#!ruby -n
puts $_

Add option 「-p」, At the end of program, execute 「puts $_」

very good

#!ruby -np

Global

$a=3

# bad
puts "$a is #{$a}"

# good
puts "$a is #$a"

STDIO

Output

# bad
w="Hello Ruby!"
puts w

# good
w="Hello Ruby!"
$><<w

---

# bad
10.times{puts:hello}

# good
puts [:hello]*10

---

$s="Ruby"

# bad
puts $s

# good
puts$s

Output(Numeric)

# bad
puts 100

# good
p 100

String

split

# bad
'hello world ruby'.split(' ') #=> ['hello', 'world', 'ruby']

# good
'hello world ruby'.split #=> ['hello', 'world', 'ruby']

---

# bad
"ruby".split('') #=> ["r", "u", "b", "y"]

# good
"ruby".chars #=> ["r", "u", "b", "y"]

char

# bad
c='a'

# good
c=?a

size

# bad
"hello\n".size-1 #=> 5

# good
"hello\n"=~/$/ #=> 5

symbol

# bad
puts"ruby"

# good
puts:ruby

match

# bad
if 'ruby'=~/r/
  puts 'hello!'
end

# good
if 'ruby'[?r]
  puts 'Hello!'
end

---

s="Hello Ruby"

# bad
s.gsub(/Ruby/){|m|puts m} #=> Ruby

# good
s.gsub(/Ruby/){puts $&} #=> Ruby

other tips

'hello'*0 #=> ''
'hello'*1 #=> 'hello'
'hello'*2 #=> 'hellohello'

Numeric

define

# bad
n=10000

# good
n=1e4 #=> 10000.0

---

# bad
n=0.0001

# good
n=1e-4 #=> 0.0001

---

# bad
a=-10

# good
a=~9

---

# bad
a=n==0?1:0

# good
a=1[n]

Radix conversion

to_s can specify radix when convert integer to string.

16.to_s     #=> "16"
16.to_s(2)  #=> "10000"
16.to_s(8)  #=> "20"
16.to_s(16) #=> "10"

get bit value

[] method can get bit value.

p 1[0] #=> 1
p 2[0] #=> 0
p 3[0] #=> 1

Bit operation

n=3

# bad
(n+1)*3 #=> 12

# good
-~n*3 #=> 12

---

n=3

# bad
(n-1)*3 #=> 6

# good
~-n*3 #=> 6

Array

Literal

# bad
a=Array.new

# good
a=[]

# bad
a=['hoge','piyo','fuga']

# good
a=%w(hoge piyo fuga)

# bad
a=[1,2,3,4,5]

# good
a=*1..5

join

# bad
[1,2,3].join('+') #=> 1+2+3

# good
[1,2,3]*?+ #=> 1+2+3

uniq

# bad
[1,1,2,2,3,3].uniq #=> [1,2,3]

# good
[1,1,2,2,3,3]|[] #=> [1,2,3]

push

# bad
[1,2,3].push(4) #=> [1, 2, 3, 4]

# good
[1,2,3]<<4 #=> [1, 2, 3, 4]

unshift

# bad
[1,2,3].unshift(4) #=> [4, 1, 2, 3]

# good
[1,2,3][0,0]=4 #=> [4, 1, 2, 3]

compact

p [nil,1,2,3,nil].compact #=> [1, 2, 3]
p [nil,1,2,3,nil]-[p]     #=> [1, 2, 3]

reverse

a=[1,2]

# bad
a.reverse #=> [2, 1]

# good
a.rotate #=> [2, 1]

sum

# bad
[1,2,3].inject(:+) #=> 6

# good
eval"[1,2,3]*?+" #=> 6

# very good (RUBY_VERSION >= 2.4)
[1,2,3].sum

other

update max value

# bad
a=[a,b+1].max

# good
a>b||a=b+1

Enumerator

n="10"
t="1"
i=0

# bad
n.to_i.times{i+=t.to_i}

# good
eval"i+=#{t};"*n.to_i

Hash

other

check odd? or even?

h={}
h[1]^=1 #=> nil^1  -> true
h[1]^=1 #=> true^1 -> false