315\. Count of Smaller Numbers After Self

Hard

You are given an integer array `nums` and you have to return a new `counts` array. The `counts` array has the property where `counts[i]` is the number of smaller elements to the right of `nums[i]`.

**Example 1:**

**Input:** nums = [5,2,6,1]

**Output:** [2,1,1,0]

**Explanation:** To the right of 5 there are **2** smaller elements (2 and 1). To the right of 2 there is only **1** smaller element (1). To the right of 6 there is **1** smaller element (1). To the right of 1 there is **0** smaller element. 

**Example 2:**

**Input:** nums = [-1]

**Output:** [0] 

**Example 3:**

**Input:** nums = [-1,-1]

**Output:** [0,0] 

**Constraints:**

*   <code>1 <= nums.length <= 10<sup>5</sup></code>
*   <code>-10<sup>4</sup> <= nums[i] <= 10<sup>4</sup></code>