README_EN.md

815. Bus Routes

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Description

We have a list of bus routes. Each routes[i] is a bus route that the i-th bus repeats forever. For example if routes[0] = [1, 5, 7], this means that the first bus (0-th indexed) travels in the sequence 1->5->7->1->5->7->1->... forever.

We start at bus stop S (initially not on a bus), and we want to go to bus stop T. Travelling by buses only, what is the least number of buses we must take to reach our destination? Return -1 if it is not possible.

Example:

Input: 

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

S = 1

T = 6

Output: 2

Explanation: 

The best strategy is take the first bus to the bus stop 7, then take the second bus to the bus stop 6.

Note:

<li><code>1 &lt;= routes.length &lt;= 500</code>.</li>

<li><code>1 &lt;= routes[i].length &lt;= 500</code>.</li>

<li><code>0 &lt;= routes[i][j] &lt; 10 ^ 6</code>.</li>

Solutions

Python3

Java

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