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. Example Input: height = [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 Input: height = [4,2,0,3,2,5] Output: 9 Constraints n == height.length 0 <= n <= 3 * 10^4 0 <= height[i] <= 10^5 Example Input height = [0,1,0,2,1,0,1,3,2,1,2,1]