Backtracking in Python with Tests

Backtracking holds 78 problems (3 Easy, 56 Medium, 19 Hard). Generate any of them into the current directory with lcpy gen -n <number>.

#	Problem	Difficulty	Solution
17	Letter Combinations of a Phone Number	Medium	solution.py
22	Generate Parentheses	Medium	solution.py
37	Sudoku Solver	Hard	solution.py
39	Combination Sum	Medium	solution.py
40	Combination Sum II	Medium	solution.py
46	Permutations	Medium	solution.py
47	Permutations II	Medium	solution.py
51	N-Queens	Hard	solution.py
52	N-Queens II	Hard	solution.py
77	Combinations	Medium	solution.py
78	Subsets	Medium	solution.py
79	Word Search	Medium	solution.py
89	Gray Code	Medium	solution.py
90	Subsets II	Medium	solution.py
93	Restore IP Addresses	Medium	solution.py
95	Unique Binary Search Trees II	Medium	solution.py
113	Path Sum II	Medium	solution.py
126	Word Ladder II	Hard	solution.py
131	Palindrome Partitioning	Medium	solution.py
140	Word Break II	Hard	solution.py
212	Word Search II	Hard	solution.py
216	Combination Sum III	Medium	solution.py
254	Factor Combinations	Medium	solution.py
257	Binary Tree Paths	Easy	solution.py
267	Palindrome Permutation II	Medium	solution.py
282	Expression Add Operators	Hard	solution.py
291	Word Pattern II	Medium	solution.py
294	Flip Game II	Medium	solution.py
301	Remove Invalid Parentheses	Hard	solution.py
306	Additive Number	Medium	solution.py
320	Generalized Abbreviation	Medium	solution.py
351	Android Unlock Patterns	Medium	solution.py
357	Count Numbers with Unique Digits	Medium	solution.py
401	Binary Watch	Easy	solution.py
411	Minimum Unique Word Abbreviation	Hard	solution.py
425	Word Squares	Hard	solution.py
465	Optimal Account Balancing	Hard	solution.py
473	Matchsticks to Square	Medium	solution.py
489	Robot Room Cleaner	Hard	solution.py
491	Non-decreasing Subsequences	Medium	solution.py
494	Target Sum	Medium	solution.py
526	Beautiful Arrangement	Medium	solution.py
638	Shopping Offers	Medium	solution.py
679	24 Game	Hard	solution.py
681	Next Closest Time	Medium	solution.py
691	Stickers to Spell Word	Hard	solution.py
698	Partition to K Equal Sum Subsets	Medium	solution.py
756	Pyramid Transition Matrix	Medium	solution.py
784	Letter Case Permutation	Medium	solution.py
797	All Paths From Source to Target	Medium	solution.py
816	Ambiguous Coordinates	Medium	solution.py
842	Split Array into Fibonacci Sequence	Medium	solution.py
949	Largest Time for Given Digits	Medium	solution.py
967	Numbers With Same Consecutive Differences	Medium	solution.py
980	Unique Paths III	Hard	solution.py
988	Smallest String Starting From Leaf	Medium	solution.py
996	Number of Squareful Arrays	Hard	solution.py
1079	Letter Tile Possibilities	Medium	solution.py
1087	Brace Expansion	Medium	solution.py
1088	Confusing Number II	Hard	solution.py
1215	Stepping Numbers	Medium	solution.py
1219	Path with Maximum Gold	Medium	solution.py
1239	Maximum Length of a Concatenated String with Unique Characters	Medium	solution.py
1255	Maximum Score Words Formed by Letters	Hard	solution.py
1258	Synonymous Sentences	Medium	solution.py
1415	The k-th Lexicographical String of All Happy Strings of Length n	Medium	solution.py
1593	Split a String Into the Max Number of Unique Substrings	Medium	solution.py
1718	Construct the Lexicographically Largest Valid Sequence	Medium	solution.py
1780	Check if Number is a Sum of Powers of Three	Medium	solution.py
1799	Maximize Score After N Operations	Hard	solution.py
1849	Splitting a String Into Descending Consecutive Values	Medium	solution.py
1863	Sum of All Subset XOR Totals	Easy	solution.py
1980	Find Unique Binary String	Medium	solution.py
2002	Maximum Product of the Length of Two Palindromic Subsequences	Medium	solution.py
2044	Count Number of Maximum Bitwise-OR Subsets	Medium	solution.py
2375	Construct Smallest Number From DI String	Medium	solution.py
2597	The Number of Beautiful Subsets	Medium	solution.py
2698	Find the Punishment Number of an Integer	Medium	solution.py

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Backtracking in Python with Tests