Backtracking

总结：

2.pic.jpg

Example:
17 Letter Combinations of a Phone Number
22 Generate Parentheses
93 Restore IP Addresses: http://www.jianshu.com/p/73235b909c01
131 Palindrome Partitioning http://www.jianshu.com/p/a2f384836efb
254 Factor Combinations http://www.jianshu.com/p/95a3854c2a80

351. Android Unlock Patterns http://www.jianshu.com/p/52db4a83afa7
     Square grid:
     79 Word Search http://www.jianshu.com/p/0da28fc9cb3e

排列：
46 Permutations
47 Permutations II
267 Palindrome Permutation II http://www.jianshu.com/p/2b029852ad35

组合：
78 Subsets
90 Subsets II
77 Combinations
39 Combination Sum
40 Combination Sum II
216 Combination Sum III http://www.jianshu.com/p/736adb14a282

Tree:

113. Path Sum II
     其他：
114. Generalized Abbreviation
115. Matchsticks to Square