「Five programming problems every Software Engineer should be able to solve in less than 1 hour」をrubyで解いてみた

answer.rb

# encoding: sjis

# 1
# using for
def sum_for(list)
    sum = 0
    for i in list
        sum += i
    end
    sum
end
# using while
def sum_while(list)
    sum = 0
    i = 0
    while i < list.length
        sum += list[i]
        i += 1
    end
    sum 
end
# using recursive call
def sum_rec(list, sum=0)
    return sum if list.empty?

    head = list.shift
    sum_rec(list, sum + head)
end

# 2
def my_zip(alist=[], blist=[], result=[])
    return result if alist.empty? && blist.empty?

    a = alist.shift
    b = blist.shift

    my_zip(alist, blist, (result << [a, b].compact).flatten)
end

# 3
def fib(n)
    case n
    when 0
        []
    when 1
        [0]
    else
        list = [0, 1]
        (n - list.length).times do 
            list[list.length] = list[-2] + list[-1]
        end
        list
    end
end

# 4
def perm_max(list=[])
    list.permutation.collect{ |i| i.map(&:to_s).join }.max.to_i
end

# 5
def comb_100(size=1)
    ["+", "-", ""]
        .repeated_permutation(size - 1)
        .to_a
        .map{ |e| (1..size).to_a.zip(e).flatten.map(&:to_s).join }
        .select{ |e| eval(e) == 100 }
end