find_smallest_available_color Function

    function find_smallest_available_color(v, graph, colors) result(color_id)
        implicit none
        integer(int32) :: color_id
        integer(int32), intent(in) :: v
        class(type_crs_adjacency_element), intent(in) :: graph
        integer(int32), intent(in) :: colors(:)

        logical, allocatable :: forbidden_colors(:)
        integer(int32) :: neighbor_color, max_possible_colors, i
        integer(int32), allocatable :: neighbors(:)
        integer(int32) :: neighbor_id

        max_possible_colors = graph%get_degree(v) + 1

        call allocate_array(forbidden_colors, length=max_possible_colors)
        forbidden_colors = .false.

        ! ゲッターで隣接要素リストを取得し、使用済み色をマーク
        neighbors = graph%get_neighbors(v)
        do i = 1, size(neighbors)
            neighbor_id = neighbors(i)
            neighbor_color = colors(neighbor_id)
            if (neighbor_color > 0 .and. neighbor_color <= max_possible_colors) then
                forbidden_colors(neighbor_color) = .true.
            end if
        end do
        call deallocate_array(neighbors)

        ! マークされていない最小の色を見つける
        color_id = 1
        do while (color_id <= max_possible_colors)
            if (.not. forbidden_colors(color_id)) then
                exit
            end if
            color_id = color_id + 1
        end do

        call deallocate_array(forbidden_colors)
    end function find_smallest_available_color