同学，余老师的课吧。。。

这个题还挺有意思的。帮你做了
gen cweight = weight in 1
replace cweight = (cweight[_n-1]+weight)*(cweight[_n-1]+weight<=300)+weight*(cweight[_n-1]+weight>300) in 2/l
gen group = 1 in 1
replace group = group[_n-1]*(cweight[_n-1]+weight<=300)+(group[_n-1]+1)*(cweight[_n-1]+weight>300) in 2/l
bys group: egen totweight = total(weight)
drop cweight
sort id