added breadth-first search

Added graph examples

Coding up trie examples

Implemented max-heap

Added binary search tree code

Coded up singly- and doubly-linked lists

Using sorting to speed up tasks

added dynamic programming exercises

added last question from ch 11

recursive exercises from chapter 11

add code to reverse a string using a stack

implemented homework exercises for hash tables

found a bug in the book's code

added insertion sort

coded up comparison of selection & bubble sorts