i'm not exactly sure either, too bad he didnt define "invert". i based my comment on the only thing I could find: https://wwwx.cs.unc.edu/~duozhao/entry/2014/1

i'm not exactly sure either, too bad he didnt define "invert". i based my comment on the only thing I could find: https://wwwx.cs.unc.edu/~duozhao/entry/2014/12/binary-tree-upside-down/ https://wwwx.cs.unc.edu/~duozhao/entry/2014/12/binary-tree-u... this is only slightly harder than the trivial (if u know recursion) "mirroring" a tree problem