#
# twosum.icn, find two array elements that add up to a given sum
# Dedicated to the public domain
#
link fullimag
procedure main(arglist)
    sum := pop(arglist) | 21
    L := []
    if *arglist > 0 then every put(L, integer(!arglist)) & L := sort(L)
    else L := [0, 2, 11, 19, 90]

    write(sum)
    write(fullimage(L))
    write(fullimage(twosum(sum, L)))
end

# assume sorted list, only interested in zero or one solution
procedure twosum(sum, L)
    i := 1
    j := *L
    while i < j do {
        try := L[i] + L[j]
        if try = sum then return [i,j]
        else
            if try < sum then
                i +:= 1
            else
                j -:= 1
    }
    return []
end