How should I practice Minimum Bus Routes to a Destination?

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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Minimum Bus Routes to a Destination

Google● HardNEW GRADONSITE INTERVIEW

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Problem statement

Each row in routes lists the distinct stops served by one bus route. Boarding a route costs one bus; after boarding, you may travel to any stop on that route and transfer to another route serving the same stop.

Return the minimum number of buses needed to travel from sourceStop to targetStop. Return 0 when the two stops are equal and -1 when the destination is unreachable.

Function

minimumBusRoutes(routes: int[][], sourceStop: int, targetStop: int) → int

Examples

Example 1

routes = [[1,2,7],[3,6,7]]sourceStop = 1targetStop = 6return = 2

Take the first route to stop 7, then transfer to the second route and reach 6.

Example 2

routes = [[1,2,3],[4,5,6]]sourceStop = 1targetStop = 6return = -1

The two routes share no stop, so no transfer connects the endpoints.

Example 3

routes = [[5,8],[8,9]]sourceStop = 5targetStop = 5return = 0

No bus is needed when the source already equals the destination.

Constraints

1 <= routes.length <= 500.
1 <= routes[i].length <= 100000.
The total number of route-stop entries is at most 200000.
Stops within one route are distinct integers in [0,10^9].
0 <= sourceStop,targetStop <= 10^9.