## Trapping Rain Water

Given `n` non-negative integers representing an elevation map where the width of each bar is `1`, compute how much water it can trap after raining.

### Examples

**Example 1:**

<p align="left">
  <img src="../../assets/rainwatertrap.png" alt="Rain water trap">
</p>

```text
Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6
Explanation: The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped.
```

**Example 2:**

```text
Input: height = [4,2,0,3,2,5]
Output: 9
```

### Constraints

- `n == height.length`
- `0 <= n <= 3 * 104`
- `0 <= height[i] <= 105`

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### Notes

- N/A