コーディングテスト用のメモ。

基礎文法

繰り返し

for

for i in 1..3 do
  puts i
end

※配列でも可

for num in [1, 2, 3] do
  puts num
end

each

[1, 2, 3, 4].each do |num|
  p num
end

while

num = 0 #初期値
while num <= 12 do #条件
  p num #処理
  num += 3 #値の更新
end

times

3.times do |num|
  p num
end

各桁の和

a = 11
puts a.to_s.split('').map{|x| x.to_i}.inject(:+)
#=> 2

String#chars

a = 11
puts a.to_s.chars.map{|x| x.to_i}.sum

### 奇数or偶数番目要素の取得

Integer#digits

a = 11
puts a.digits.sum

条件分岐(書き換えパターン)

pattern(1)

s = "hoge"
if s==hoge
  puts "YES"
else
  puts "NO"
end

#=>YES

pattern(2)

s = "hoge"
puts s == hoge ? "YES":"NO"

#=>YES

pattern(3)

s = "hoge"
case s
when "hoge" then
  puts "YES"
when "no_hoge" then
  puts "NO"

#=>YES

.gsub(パターンマッチング)

string = "ruby ruby ruby"
puts string.gsub(/ruby/, 'python')

#=> python python python

数値の切り捨て

1.4.floor # 1
1.5.floor # 1
-1.4.floor # -2
-1.5.floor # -2

数値の切り上げ

1.4.ceil  # 2
1.5.ceil  # 2
-1.4.ceil # -1
-1.5.ceil # -1

配列の操作

配列の割り算

a = [2, 4, 6]
b = a.map(|x| x/2)
puts b

#=> [1, 2, 3]

配列の合計

a = [1, 2, 3]
puts a.inject(:+)

#=> 6

ary = ('a'..'j').to_a
#=> ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"]

# 偶数番目
ary.select.with_index { |_, i| i.even? }
#=> ["a", "c", "e", "g", "i"]

# 奇数番目
ary.select.with_index { |_, i| i.odd? }
#=> ["b", "d", "f", "h", "j"]

並べ替え

ary = [2, 4, 1, 5, 3]

# 昇順 
ary.sort
#=> [1, 2, 3, 4, 5]

# 降順
ary.sort.reverse
#=> [5, 4, 3, 2, 1]

重複要素を統一

ary = [1, 2, 2, 3, 3]

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

配列→文字列

ary = [1, 2, 3, 4, 5]

ary.join(' ')
#=> '1 2 3 4 5'

要素の追加

ary = ['a', 'b', 'c']

ary << 'd'
#=> ['a', 'b', 'c', 'd']

最大値最小値

ary = [1, 25, 50, 75, 100]

ary.minmax
#=> [1, 100]