leetcode 407

문제 설명Given 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. 문제 예제Example 1:Input: heightMap = [[1,4,3,1,3,2],[3,2,1,3,2,4],[2,3,3,2,3,1]]Output: 4Explanation: 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 ..