在两个不同向量之间交替选择，同时确保每个选择都大于前一个

I need to select numbers alternating between two different vectors. First I select the smallest number globally, then depending where the first number came from the next one needs to come from the other vector and be larger than the selection prior. Meaning at each new selection I have to do two things. 1) the number has to come from the other vector 2) it has to be greater than the last selection.I need to select numbers alternating between tw