Practice Bus Routes

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Hard#815

LeetCode Problem

Bus Routes

Array Hash Table Breadth-First Search

Problem Statement

You are given an array routes representing bus routes where routes[i] is a bus route that the ith bus repeats forever. You will start at the bus stop source (You are not on any bus initially), and you want to go to the bus stop target. You can travel between bus stops by buses only. Return the least number of buses you must take to travel from source to target. Return -1 if it is not possible.

Source: Bus Routes on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

routes = [[1,2,7],[3,6,7]], source = 1, target = 6

Output

# Example 2

Input

routes = [[7,12],[4,5,15],[6],[15,19],[9,12,13]], source = 15, target = 12

Output

-1

Constraints

1 <= routes.length <= 500.

1 <= routes[i].length <= 10^5

All the values of routes[i] are unique.

sum(routes[i].length) <= 10^5

0 <= routes[i][j] < 10^6

0 <= source, target < 10^6

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