• contains duplicate
• balanced_binary_tree
• binary_search
• binary_tree_level_order_traversal
• buy_sell_stock
• contains_duplicate
• group_anagrams
• maximum_depth_of_binary_tree
• minimum_stack
• number_of_islands
• reverse_words
• same_tree
• search_2d_matrix
• spiral_matrix
• symmetric_tree
• top_k_frequent_elements
• two_sums
• valid_anagram