How should I practice Grid Robot Route with Charging Priorities?

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

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Grid Robot Route with Charging Priorities

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Problem statement

A robot travels through a rectangular grid from its unique S cell to its unique T cell. A cell is one of S, T, . (ordinary open space), C (a charging cell), or # (a wall).

Each move goes up, down, left or right to a non-wall cell and consumes one unit of battery. There are no diagonal moves. The robot starts with a full battery of a capacity that you must determine. Whenever it enters a C cell, it automatically refills to that capacity and the number of charging visits increases by one. Refilling is mandatory on entry, even on a repeated visit. The move into a charger still costs one unit, but arriving with exactly zero battery is allowed before refilling.

For a route, the required battery capacity is the largest number of moves in any segment from the start or a charging visit to the next charging visit or the target. The initial full battery is not a charging visit. Revisiting S does not refill the battery. The journey ends immediately on reaching T.

Compare routes by the following priorities, in this order:

Minimize the number of charging visits.
Among routes with that minimum, minimize the required battery capacity.
Among routes tied on both preceding values, minimize the total number of moves.

Return these three optimal values as [chargingVisits, requiredCapacity, totalMoves]. Return [-1, -1, -1] if no route reaches the target. Return the values only, not the route's coordinates. Cells may be revisited, but every charger entry is counted; there is no free option to pass through a charger without refilling.

Function

optimalChargingCost(grid: String[]) → int[]

Examples

Example 1

grid = ["SCT","..."]return = [0,4,4]

The direct two-move route enters the charger, giving [1,1,2]. Going around the bottom uses no charger and gives [0,4,4], which wins because charging visits have first priority.

Example 2

grid = ["SC...",".###.",".###T",".C..."]return = [1,4,8]

The top-and-right corridor takes six moves and visits the top charger after one move, so it needs capacity five. The left-and-bottom corridor takes eight moves and reaches its charger after four moves, giving two four-move segments. Both use one charger, so [1,4,8] beats [1,5,6].

Constraints

The grid has from 1 through 10 rows and from 1 through 10 columns, with at least 2 cells in total.
Every row has the same length and contains only S, T, ., C and #.
There is exactly one S and one T; they are distinct cells.
There are at most 8 charging cells. The robot cannot leave the grid or enter walls.