Create ReconstructItinerary.java

Author: leo414

ReconstructItinerary.java

@@ -0,0 +1,90 @@
+package leetcode;
+
+import java.util.*;
+
+/**
+ * Project Name : Leetcode
+ * Package Name : leetcode
+ * File Name : ReconstructItinerary
+ * Creator : Leo
+ * Description : 332. Reconstruct Itinerary
+ */
+public class ReconstructItinerary {
+
+    /**
+     * Given a list of airline tickets represented by pairs of departure and arrival airports [from, to],
+     * reconstruct the itinerary in order. All of the tickets belong to a man who departs from JFK.
+     * Thus, the itinerary must begin with JFK.
+
+     Note:
+     If there are multiple valid itineraries, you should return the itinerary that
+     has the smallest lexical order when read as a single string. For example,
+     the itinerary ["JFK", "LGA"] has a smaller lexical order than ["JFK", "LGB"].
+     All airports are represented by three capital letters (IATA code).
+     You may assume all tickets form at least one valid itinerary.
+
+     Example 1:
+     tickets = [["MUC", "LHR"], ["JFK", "MUC"], ["SFO", "SJC"], ["LHR", "SFO"]]
+     Return ["JFK", "MUC", "LHR", "SFO", "SJC"].
+
+     Example 2:
+     tickets = [["JFK","SFO"],["JFK","ATL"],["SFO","ATL"],["ATL","JFK"],["ATL","SFO"]]
+     Return ["JFK","ATL","JFK","SFO","ATL","SFO"].
+
+     Another possible reconstruction is ["JFK","SFO","ATL","JFK","ATL","SFO"].
+     But it is larger in lexical order.
+
+
+     DFS(HashMap) + PriorityQueue
+
+     JFK   SFO
+            |
+         ATL
+
+
+     time : O(nlogn)
+     space : O(n)
+
+     */
+
+    HashMap<String, PriorityQueue<String>> map;
+    List<String> res;
+
+    public List<String> findItinerary(String[][] tickets) {
+        map = new HashMap<>();
+        res = new LinkedList<>();
+        for (String[] ticket : tickets) {
+            map.computeIfAbsent(ticket[0], k -> new PriorityQueue<>()).add(ticket[1]);
+        }
+        helper("JFK");
+        return res;
+    }
+
+    private void helper(String airport) {
+        while (map.containsKey(airport) && !map.get(airport).isEmpty()) {
+            helper(map.get(airport).poll());
+        }
+        res.add(0, airport);
+    }
+
+    public List<String> findItinerary2(String[][] tickets) {
+        HashMap<String, PriorityQueue<String>> map = new HashMap<>();
+
+        for (String[] ticket : tickets) {
+            map.computeIfAbsent(ticket[0], k -> new PriorityQueue()).add(ticket[1]);
+        }
+
+        List<String> res = new LinkedList();
+        Stack<String> stack = new Stack<>();
+        stack.push("JFK");
+
+        while (!stack.empty()) {
+            while (map.containsKey(stack.peek()) && !map.get(stack.peek()).isEmpty()) {
+                stack.push(map.get(stack.peek()).poll());
+            }
+            res.add(0, stack.pop());
+        }
+
+        return res;
+    }
+}