Árvores AVL

links para materiais diversos sobre árvores AVL
https://www.cs.usfca.edu/~galles/visualization/AVLtree.html
https://www.tutorialspoint.com/data_structures_algorithms/avl_tree_algorithm.htm https://courses.cs.washington.edu/courses/cse332/10sp/lectures/lecture7.pdf
http://visualgo.net/bst
https://en.wikipedia.org/wiki/AVL_tree
https://www.cs.purdue.edu/homes/ayg/CS251/slides/chap7b.pdf
http://www.geeksforgeeks.org/avl-tree-set-1-insertion/