Add implementation for itinerary reconstruction from tickets using HashMap

Author: gourabofficial

Hashing/Question/ItineraryFromTTickets.java

@@ -0,0 +1,40 @@
+import java.util.HashMap;
+
+public class ItineraryFromTTickets {
+    public static void main(String[] args) {
+        HashMap<String, String> tickets = new HashMap<>();
+        tickets.put("Chennai", "Bangalore");
+        tickets.put("Mumbai", "Delhi");
+        tickets.put("Goa", "Chennai");
+        tickets.put("Delhi", "Goa");
+
+        findItinerary(tickets);
+    }
+
+    public static void findItinerary(HashMap<String, String> ticket) {
+        HashMap<String, String> reverseMap = new HashMap<>();
+
+        // step 1 reverse map
+        for (String from : ticket.keySet()) {
+            String to = ticket.get(from);
+            reverseMap.put(to, from);
+        }
+
+        // find the starting city
+        String start = "";
+        for (String from : ticket.keySet()) {
+            if (!reverseMap.containsKey(from)) {
+                start = from;
+                break;
+            }
+        }
+
+        System.out.print("Itinerary: ");
+        while (ticket.containsKey(start)) {
+            System.out.print(start + " → ");
+            start = ticket.get(start);
+        }
+        System.out.println(start);
+    }
+
+}

Hashing/Question/UnionOfTwoArrays.java

@@ -1,3 +1,4 @@
+//it meanse the two array there is some value after completed the operation the output is : 1,2,3,4,5,6,10 (// ignore the same value )
 
 import java.util.HashSet;