Add C++ solutions for Chapter 13 (Graphs)

[ongshunping]

• bipartite_graph_validation.cpp
• connect_the_dots.cpp
• count_islands.cpp
• graph_deep_copy.cpp
• longest_increasing_path.cpp
• matrix_infection.cpp
• merging_communities.cpp
• prerequisites.cpp
• shortest_path.cpp
• shortest_transformation_sequence.cpp
• shortest_transformation_sequence_optimized.cpp

union was renamed to unionSets because union is a reserved keyword in C++

[Destiny-02]

Please rename function to match python

[ongshunping]

In C++, union is a reserved keyword and using it as an identifier will cause a compilation error. I suggest using union_ to match Python's naming. Let me know if you prefer union or other names.

[Destiny-02]

Please delete the other 2 constructors to match python

[ongshunping]

Done

[Destiny-02]

Please update function name to match python

[ongshunping]

In C++, union is a reserved keyword and using it as an identifier will cause a compilation error. I suggest using union_ to match Python's naming. Let me know if you prefer union or other names.

[Destiny-02]

I think i is a better name than unused in this case

[ongshunping]

Done