Add questions about permutation:
1. C1_73A_AllPermutations: get all the permutation of a given int array
2. C1_73B_NextPermutation: get the next permutation in lexicographically
order.
3. C1_73C_PermutationSequence: get the k-th permutation in the
permutations in lexicographically order
4. C1_73D_UniquePermutation: get unique permutations
when the int array have duplications.