All O`one Data Structure

Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the `AllOne` class: - `AllOne()` Initializes the object of the data structure. - `inc(String key)` Increments the count of the string `key` by `1`. If `key` does not exist in the data structure, insert it with count `1`. - `dec(String key)` Decrements the count of the string `key` by `1`. If the count of `key` is `0` after the decrement, remove it from the data structure. It is guaranteed that `key` exists in the data structure before the decrement. - `getMaxKey()` Returns one of the keys with the maximal count. If no element exists, return an empty string `""`. - `getMinKey()` Returns one of the keys with the minimum count. If no element exists, return an empty string `""`. **Note** that each function must run in `O(1)` average time complexity.   **Example 1:** **Input** ["AllOne", "inc", "inc", "getMaxKey", "getMinKey", "inc", "getMaxKey", "getMinKey"] [[], ["hello"], ["hello"], [], [], ["leet"], [], []] **Output** [null, null, null, "hello", "hello", null, "hello", "leet"] **Explanation** AllOne allOne = new AllOne(); allOne.inc("hello"); allOne.inc("hello"); allOne.getMaxKey(); // return "hello" allOne.getMinKey(); // return "hello" allOne.inc("leet"); allOne.getMaxKey(); // return "hello" allOne.getMinKey(); // return "leet" ```   **Constraints:** - `1 <= key.length <= 10` - `key` consists of lowercase English letters. - It is guaranteed that for each call to `dec`, `key` is existing in the data structure. - At most `5 * 104` calls will be made to `inc`, `dec`, `getMaxKey`, and `getMinKey`.