9.7. - wrote a tree class and used it
mystack_8_1 - deque realization in a separate file
9.5. - with function next_inorder_node in a separate file. looks ugly still=(
7.2. (cycle in linked list) - variant after a hint, in a separate file.
10.8. - running median.
12.9 - if a letter can be written using text
13.5 - common elems of two sorted arrays without duplicates