add a solution for 841

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_841.java

@@ -5,6 +5,7 @@
 import java.util.List;
 import java.util.Queue;
 import java.util.Set;
+import java.util.TreeSet;
 
 public class _841 {
     public static class Solution1 {
@@ -34,4 +35,27 @@ public boolean canVisitAllRooms(List<List<Integer>> rooms) {
             return unvisitedRooms.isEmpty();
         }
     }
+
+    public static class Solution2 {
+        public boolean canVisitAllRooms(List<List<Integer>> rooms) {
+            TreeSet<Integer> treeSet = new TreeSet<>();
+            Set<Integer> visited = new HashSet<>();
+            visited.add(0);
+            treeSet.addAll(rooms.get(0));
+            while (!treeSet.isEmpty()) {
+                Integer key = treeSet.pollFirst();
+                if (!visited.add(key)) {
+                    continue;
+                }
+                if (visited.size() == rooms.size()) {
+                    return true;
+                }
+                treeSet.addAll(rooms.get(key));
+            }
+            if (visited.size() == rooms.size()) {
+                return true;
+            }
+            return false;
+        }
+    }
 }

src/test/java/com/fishercoder/_841Test.java

@@ -12,11 +12,13 @@
 
 public class _841Test {
     private static _841.Solution1 solution1;
+    private static _841.Solution2 solution2;
     private static List<List<Integer>> rooms;
 
     @BeforeClass
     public static void setup() {
         solution1 = new _841.Solution1();
+        solution2 = new _841.Solution2();
     }
 
     @Test
@@ -27,6 +29,7 @@ public void test1() {
         rooms.add(Arrays.asList(3));
         rooms.add(Arrays.asList());
         assertEquals(true, solution1.canVisitAllRooms(rooms));
+        assertEquals(true, solution2.canVisitAllRooms(rooms));
     }
 
     @Test
@@ -37,5 +40,6 @@ public void test2() {
         rooms.add(Arrays.asList(2));
         rooms.add(Arrays.asList(0));
         assertEquals(false, solution1.canVisitAllRooms(rooms));
+        assertEquals(false, solution2.canVisitAllRooms(rooms));
     }
 }