partition Function

    function partition(array, left, right, pindex)
        integer, pointer :: array(:)
        integer, intent(in)    :: left, right, pindex

        integer :: partition

        integer :: pvalue, tmp, sindex, i

        pvalue = array(pindex)
        tmp = array(right)
        array(right) = pvalue
        array(pindex) = tmp

        sindex = left

        do i = left, right-1
            if(array(i) .le. pvalue) then
                tmp = array(i)
                array(i) = array(sindex)
                array(sindex) = tmp
                sindex = sindex + 1
            endif
        end do

        tmp = array(sindex)
        array(sindex) = array(right)
        array(right) = tmp
        partition = sindex
    end function partition