Update README.md

Update README.md

solutions to 3 and 4

Update README.md

Update README.md

python3 solution to trees added

Added C++ hash table solutions

Added C++ tree solutions

Workshop 5 Big O Links

Python solutions for Workhsop 5

renaming of big O workshop folder

Updated Rest of cpp Problems

Update Problem3_Add_Digits.cpp

Update Problem2_Missing_Number.cpp

Update Problem1_Valid_Anagram.cpp