How should I practice Minimum Distance to Return a Book?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google onsite interview problems in FastPrep.

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FastPrep tags this as a Google onsite interview coding practice problem when the problem catalog has that company and stage context.

Minimum Distance to Return a Book

Google● MediumINTERNONSITE INTERVIEW

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Problem statement

You are given a rectangular map grid, a starting coordinate start, and the direct train distance from every train station to its closest library.

Each cell in grid is one of:

., an open cell;
#, a blocked cell;
L, a library; or
T, a train station.

You may walk one cell up, down, left, or right at a cost of 1, staying inside the map and never entering a blocked cell. Libraries and train stations are walkable.

The values in stationToLibrary correspond to the T cells in row-major order. Reaching a train station lets you immediately finish the trip at that station's closest library for the corresponding additional train distance.

Return the minimum total distance needed to return the book. A valid trip either walks directly onto a library or walks to a train station and then uses its direct connection. Return -1 when neither option is reachable.

Function

minimumLibraryReturnDistance(grid: String[], start: int[], stationToLibrary: int[]) → int

Examples

Example 1

grid = ["...L",".##.","T..."]start = [0,0]stationToLibrary = [2]return = 3

Walking right three times reaches the library at [0,3]. Walking two steps to the station and then traveling distance 2 would cost 4.

Example 2

grid = ["L###","###T","...."]start = [2,0]stationToLibrary = [2]return = 6

The library cannot be reached by walking. The station at [1,3] is four walking steps away, and its direct train distance is 2.

Example 3

grid = ["L#T","###","..."]start = [2,1]stationToLibrary = [3]return = -1

The blocked middle row separates the start from both the library and the train station.

Constraints

1 <= grid.length and 1 <= grid[row].length.
All rows have the same length, and the map contains at most 200000 cells.
Every cell is one of ., #, L, or T.
The map contains at least one library.
start is an in-bounds coordinate whose cell is not blocked.
stationToLibrary.length equals the number of train stations.
0 <= stationToLibrary[i] <= 10^9.