407. Trapping Rain Water II Hard 2775 64 ? Add to List Share Given an m x n integer matrix heightMap representing the height of each unit cell in a 2D elevation map, return the volume of water it can trap after raining. Example 1: Input: heightMap = [[1,4,3,1,3,2], [3,2,1,3,2,4], [2,3,3,2,3,1]] Output: 4 Explanation: After the rain, water is trapped between the blocks. We have two small ponds 1 and 3 units trapped. The total volume of water trapped is 4. |||rExample 2: Input: heightMap Output: 10 Constraints: = [[3,3,3,3,3],[3,2,2,2,3], [3,2,1,2,3], [3,2,2,2,3], [3,3,3,3,3]] m == heightMap.length n == heightMap[i].length 1 <= m, n <= 200 <= heightMap[i][j] <= 2 * 104