2349\. Design a Number Container System

Medium

Design a number container system that can do the following:

*   **Insert** or **Replace** a number at the given index in the system.
*   **Return** the smallest index for the given number in the system.

Implement the `NumberContainers` class:

*   `NumberContainers()` Initializes the number container system.
*   `void change(int index, int number)` Fills the container at `index` with the `number`. If there is already a number at that `index`, replace it.
*   `int find(int number)` Returns the smallest index for the given `number`, or `-1` if there is no index that is filled by `number` in the system.

**Example 1:**

**Input**

["NumberContainers", "find", "change", "change", "change", "change", "find", "change", "find"]

[[], [10], [2, 10], [1, 10], [3, 10], [5, 10], [10], [1, 20], [10]]

**Output:** [null, -1, null, null, null, null, 1, null, 2]

**Explanation:**

    NumberContainers nc = new NumberContainers();
    nc.find(10); // There is no index that is filled with number 10. Therefore, we return -1.
    nc.change(2, 10); // Your container at index 2 will be filled with number 10.
    nc.change(1, 10); // Your container at index 1 will be filled with number 10.
    nc.change(3, 10); // Your container at index 3 will be filled with number 10.
    nc.change(5, 10); // Your container at index 5 will be filled with number 10.
    nc.find(10); // Number 10 is at the indices 1, 2, 3, and 5. Since the smallest index that is filled with 10 is 1, we return 1.
    nc.change(1, 20); // Your container at index 1 will be filled with number 20. Note that index 1 was filled with 10 and then replaced with 20.
    nc.find(10); // Number 10 is at the indices 2, 3, and 5. The smallest index that is filled with 10 is 2. Therefore, we return 2. 

**Constraints:**

*   <code>1 <= index, number <= 10<sup>9</sup></code>
*   At most <code>10<sup>5</sup></code> calls will be made **in total** to `change` and `find`.