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.
n == height.length1 <= n <= 2 × 10^40 <= height[i] <= 10^5height = [0,1,0,2,1,0,1,3,2,1,2,1]6height = [4,2,0,3,2,5]9