Add solution to problem: Substring with concatenation of all words...
Add solution to problem: implement strstr()...
Add solution to problem: Gray Code...
Add solution to problem: subsets II...
Add problem description...
Add solution: Reverse Nodes In K-Group...
Add problem description..
Add problem: Valid Number...
add problem description...
Add problem: count and say...
Add Problem: Scramble String..
improve the solution of flatten the tree to linkedlist...
Add problem descriptions...
Improved solutions to Permutations...
Improve solutions to Permutations II...
Merge branch 'master' of github.com:CharleneJiang/InterviewPuzzle