solves #332: Reconstruct Itinerary in java

Author: anishLearnsToCode

Diff for: README.md

@@ -277,6 +277,7 @@
 | 328  | [Odd Even Linked List](https://leetcode.com/problems/odd-even-linked-list)                                                                                             |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 331  | [Verify Preorder Serialization of a Binary Tree](https://leetcode.com/problems/verify-preorder-serialization-of-a-binary-tree)                                         |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 331  | 🔒 [Largest BST Subtree](https://leetcode.com/problems/largest-bst-subtree)                                                                                            |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 332  | [Reconstruct Itinerary](https://leetcode.com/problems/reconstruct-itinerary)                                                                                           |                                                                                    [![Java](assets/java.png)](src/ReconstructItinerary.java)                                                                                     |                                                                                                                                   |
 | 334  | [Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence)                                                                         |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 337  | [House Robber III](https://leetcode.com/problems/increasing-triplet-subsequence)                                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 338  | [Counting Bits](https://leetcode.com/problems/counting-bits/)                                                                                                          |                                                            [![Java](assets/java.png)](src/CountingBits.java) [![Python](assets/python.png)](python/counting_bits.py)                                                             |                                                                                                                                   |

Diff for: src/ReconstructItinerary.java

@@ -0,0 +1,40 @@
+// https://leetcode.com/problems/reconstruct-itinerary
+// E = |flights|, V = |airports| N = E / V
+// T: O(V * NlogN) = O(E log(E / V))
+// S: O(V + E)
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.PriorityQueue;
+import java.util.Queue;
+
+public class ReconstructItinerary {
+    public List<String> findItinerary(List<List<String>> tickets) {
+        final Map<String, Queue<String>> graph = createGraph(tickets);
+        final List<String> result = new ArrayList<>();
+        dfs(graph, "JFK", result);
+        return result.reversed();
+    }
+
+    private static void dfs(Map<String, Queue<String>> graph, String current, List<String> result) {
+        final Queue<String> queue = graph.getOrDefault(current, new PriorityQueue<>());
+        while (!queue.isEmpty()) {
+            final String to = queue.poll();
+            dfs(graph, to, result);
+        }
+        result.add(current);
+    }
+
+    private static Map<String, Queue<String>> createGraph(List<List<String>> tickets) {
+        final Map<String, Queue<String>> graph = new HashMap<>();
+        for (List<String> ticket : tickets) {
+            final String from = ticket.get(0), to = ticket.get(1);
+            final Queue<String> queue = graph.getOrDefault(from, new PriorityQueue<>());
+            queue.add(to);
+            graph.putIfAbsent(from, queue);
+        }
+        return graph;
+    }
+}