Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Explanation: The elevation map represents various bar heights. Water fills the depressions. For instance, between heights 2 and 3, there's a depression of 1 unit at index 5 (height 0), trapping (min(2,3) - 0) = 2 units. Similarly for other spots, totaling 6 units.