// Trapping Rain Water — HARD

// Category: array

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.

Hint: For each position, the water trapped equals `min(maxLeft, maxRight) - height[i]`. Use two pointers for an O(n) solution.

Example: height = [0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]

Output: 6