public class AllOne
extends Object
432 - All O\`one Data Structure\.
Hard
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 `""`.
**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`.