function generate_sorted_matrix(m, n)::Matrix{Int}
    v = abs.(rand(Int, m*n)) .% 1000
    sort!(v)
    reshape(v, m, n)
end

const Option{T} = Union{Some{T}, Nothing}

function find_in_sorted_array(V::AbstractVector{Int}, n::Int)::Option{Int}
    lo, mid, hi = 1, round(Int, length(V)/2), length(V)
    while lo < hi
        if n < V[mid]
            hi = mid-1
            mid = round(Int, (lo+hi)/2)
            continue
        elseif n > V[mid]
            lo = mid+1
            mid = round(Int, (lo+hi)/2)
            continue
        elseif n == V[mid]
            return Some(mid)
        end
        @assert false "if exhausted"
    end
    V[mid] == n ? Some(mid) : nothing
end

function find_in_sorted_matrix(M::Matrix, n::Int)::Option{Tuple{Int, Int}}
    r, c = size(M)
    # 1. Find column
    lo, mid, hi = 1, round(Int, c/2), c
    while lo < hi
        if n < M[begin, mid]
            hi = mid-1
            mid = round(Int, (lo+hi)/2)
            continue
        elseif n > M[end, mid]
            lo = mid+1
            mid = round(Int, (lo+hi)/2)
            continue
        else
            break
        end
    end
    # 2. Find element
    in_array = find_in_sorted_array((@view M[:,mid]), n)
    if isnothing(in_array)
        nothing
    else
        Some((mid, something(in_array)))
    end
end