Question

Give an array, how to find next unused number?

["10", "2", "3", "5", "6", "7"], it should return "4"

["1", "2", "3"], it should return "4".

Answer 1

Here you go:

def next_unused(ary)
    sary = ary.collect(&:to_i).sort
    i = 0
    s = sary[0]
    # puts "ary: #{sary.inspect}, s: #{s}"
    while (i<sary.size && (s == sary[i])) do
        # puts "s:#{s}, sary:#{sary[i]}"
        s += 1
        i += 1
    end
    s.to_s
end