This problem is a variation of the famous Eulerian path problem in graph theory. It involves traversing a graph such that each edge is crossed exactly once. The islands represent vertices, and the bridges represent edges in the graph.

Key points:

1. The tourist crossed each bridge exactly once, which implies we are dealing with an Eulerian path.
2. An Eulerian path exists if exactly two vertices have an odd degree (the number of edges/bridges connected to them is odd), and all other vertices have even degrees.
3. The tourist visited the island "Tridweep" exactly 3 times but neither started nor ended on "Tridweep."

Step-by-step analysis:

• The number of times a vertex (island) is visited must be correlated with its degree. For instance, every time the tourist visits an island, they enter through one bridge and leave through another, meaning each visit uses 2 bridges.

• If the tourist visited "Tridweep" 3 times, they must have entered and exited it 3 times. Thus, 6 trips (3 entries and 3 exits) correspond to visiting Tridweep.

  However, since the tourist neither started nor ended on "Tridweep," all the visits to Tridweep are through entering and leaving, which implies the total number of bridges connected to Tridweep is 6.

Conclusion:

The island "Tridweep" is connected by 6 bridges.

Would you like further details or have any questions? Here are some follow-up related questions:

1. What are the conditions for an Eulerian circuit?
2. How would the problem change if the tourist started or ended on "Tridweep"?
3. Can an Eulerian path exist if all vertices have even degrees?
4. How can graph theory be used to solve real-world problems involving networks?
5. What other problems in mathematics relate to the Eulerian path or circuit?

Tip: Euler's work on the Seven Bridges of Königsberg is a foundational study in graph theory that introduced the concept of Eulerian paths.