From fea63bf5622a37387b1cf2f2f5ab680c53d9bf31 Mon Sep 17 00:00:00 2001
From: Liqun Li <liqlee@gmail.com>
Date: Mon, 30 May 2022 13:58:34 -0700
Subject: [PATCH] leetcode 815: Bus-Routes: updated/added a java solution

---
 BFS/815.Bus-Routes/815.Bus-Routes.java | 45 ++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 BFS/815.Bus-Routes/815.Bus-Routes.java

diff --git a/BFS/815.Bus-Routes/815.Bus-Routes.java b/BFS/815.Bus-Routes/815.Bus-Routes.java
new file mode 100644
index 000000000..a19b6db1a
--- /dev/null
+++ b/BFS/815.Bus-Routes/815.Bus-Routes.java
@@ -0,0 +1,45 @@
+class Solution {
+  public int numBusesToDestination(int[][] routes, int source, int target) {
+    if (source == target)
+      return 0;
+    
+    int maxStop = -1;
+    for (int [] r : routes)
+      for (int stp : r)
+        maxStop = Math.max(maxStop, stp);
+    
+    if (target > maxStop)
+      return -1;
+    
+    int rtLen = routes.length;
+    int [] stops = new int [maxStop + 1];
+    Arrays.fill(stops, rtLen + 1);
+    
+    stops[source] = 0;
+    boolean isUpdated = true;
+    
+    while (isUpdated) {
+      
+      isUpdated = false;
+      for (int [] rt : routes) {
+        
+        int numberOfBuses = rtLen + 1;
+        for (int stp : rt)
+          
+          if ( stops[stp] < numberOfBuses )
+            numberOfBuses = stops[stp];
+        
+        numberOfBuses ++;
+        
+        for (int stp : rt)
+          if (stops[stp] > numberOfBuses) {
+            stops[stp] = numberOfBuses;
+            isUpdated = true;
+          }
+      }
+    }
+    
+    return stops[target] != rtLen + 1 ?stops[target] : -1;
+
+  }
+}