Added longest substring without repeat
http://leetcode.com/2011/05/longest-substring-without-repeating-characters.html
c string permutation
http://www.geeksforgeeks.org/write-a-c-program-to-print-all-permutations-of-a-given-string/
8 queens problem in c
http://en.literateprograms.org/Eight_queens_puzzle_(C)