How should I practice Trapping Rain Water II?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Bloomberg LP phone screen problems in FastPrep.

Is Trapping Rain Water II associated with Bloomberg LP?

FastPrep tags this as a Bloomberg LP phone screen coding practice problem when the problem catalog has that company and stage context.

Trapping Rain Water II

Bloomberg LP● HardNEW GRADPHONE SCREEN

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Problem statement

You are given an m x n integer matrix heightMap, where each value is the height of one unit-width cell in a two-dimensional terrain.

After rain falls, water can remain above a cell only when surrounding terrain prevents it from flowing to the outer boundary.

Return the total volume of trapped water.

Function

trapRainWater(heightMap: int[][]) → int

Examples

Example 1

heightMap = [[1,4,3,1,3,2],[3,2,1,3,2,4],[2,3,3,2,3,1]]return = 4

The boundary-driven water level traps four units across the two interior low regions.

Example 2

heightMap = [[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]]return = 10

The boundary height is three. The eight height-two cells hold one unit each, and the center holds two.

Example 3

heightMap = [[1,1,1],[1,0,1],[1,1,1]]return = 1

The center cell is enclosed by height-one boundary cells.

Constraints

1 <= m, n <= 200.
m * n <= 40000.
0 <= heightMap[i][j] <= 20000.