Graph in Python with Tests

Graph holds 26 problems (17 Medium, 9 Hard). Generate any of them into the current directory with lcpy gen -n <number>.

#	Problem	Difficulty	Solution
133	Clone Graph	Medium	solution.py
207	Course Schedule	Medium	solution.py
210	Course Schedule II	Medium	solution.py
261	Graph Valid Tree	Medium	solution.py
269	Alien Dictionary	Hard	solution.py
277	Find the Celebrity	Medium	solution.py
310	Minimum Height Trees	Medium	solution.py
323	Number of Connected Components in an Undirected Graph	Medium	solution.py
444	Sequence Reconstruction	Medium	solution.py
499	The Maze III	Hard	solution.py
505	The Maze II	Medium	solution.py
631	Design Excel Sum Formula	Hard	solution.py
924	Minimize Malware Spread	Hard	solution.py
928	Minimize Malware Spread II	Hard	solution.py
1059	All Paths from Source Lead to Destination	Medium	solution.py
1129	Shortest Path with Alternating Colors	Medium	solution.py
1135	Connecting Cities With Minimum Cost	Medium	solution.py
1136	Parallel Courses	Medium	solution.py
1168	Optimize Water Distribution in a Village	Hard	solution.py
1245	Tree Diameter	Medium	solution.py
1361	Validate Binary Tree Nodes	Medium	solution.py
1368	Minimum Cost to Make at Least One Valid Path in a Grid	Medium	solution.py
2127	Maximum Employees to Be Invited to a Meeting	Hard	solution.py
2493	Divide Nodes Into the Maximum Number of Groups	Hard	solution.py
3108	Minimum Cost Walk in Weighted Graph	Hard	solution.py
3481	Apply Substitutions	Medium	solution.py