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Q815.BusRoutes.cs
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Q815.BusRoutes.cs
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public class Solution {
public int NumBusesToDestination(int[][] routes, int source, int target) {
Dictionary<int, List<int>> routeDictionary = new Dictionary<int, List<int>>();
Queue<(int stop, int length)> queue = new Queue<(int stop, int length)>();
queue.Enqueue((source, 0));
for (int i = 0; i < routes.Length; i++)
{
for (int j = 0; j < routes[i].Length; j++)
{
if (!routeDictionary.ContainsKey(routes[i][j]))
{
routeDictionary.Add(routes[i][j], new List<int>());
}
//I can take which buses to a stop
routeDictionary[routes[i][j]].Add(i);
}
}
HashSet<int> visitedBuses = new HashSet<int>();
HashSet<int> visitedStops = new HashSet<int>();
while (queue.Any())
{
var item = queue.Dequeue();
if (item.stop == target)
return item.length;
foreach (var bus in routeDictionary[item.stop])
{
if (visitedBuses.Contains(bus)) continue;
visitedBuses.Add(bus);
for (int i = 0; i < routes[bus].Length; i++)
{
if (visitedStops.Contains(routes[bus][i])) continue;
visitedStops.Add(routes[bus][i]);
queue.Enqueue((routes[bus][i], item.length + 1));
}
}
}
return -1;
}
}