algo4: Revisited all permuataion related
    -- dfs: permuataion
    -- dfs: permutations_II
    -- math: next_permutation
    -- math: permutation_sequence
algo4: dfs: combination: New division and revisited
algo4: bitmanip: gray_code: Revisited
algo4: math: permutation_sequence_n_k: Revisited
algo4: twopointers: two_sum: Revisited