Input : root = [1, 2, 3, 4, null, 5, 6, null, 7]. target = 1 Output : 3 Explanation :The node with value 1 is set on fire. In 1st second it burns node 2 and node 3. In 2nd second it burns nodes 4, 5, 6. In 3rd second it burns node 7.

Input : root = [1, 2, 3, null, 5, null, 4], target = 4 Output : 4 Explanation : node with value 4 is set on fire. In 1st second it burns node 3. In 2nd second it burns node 1. In 3rd second it burns node 2. In 4th second it burns node 5.

Disclaimer: Here is the practice link to help you assess your knowledge better. It's highly recommend trying to solve it before looking at the solution.

Approach

Algorithm

Imagine each room in a house is connected by doors to its adjacent rooms (left child, right child, and the one you came from is parent). If a fire starts in one room, it spreads to all connected rooms every second. So, we convert this structure into a network (graph), where each room (node) knows which other rooms it connects to. Then, we perform a level-order BFS starting from the burning room and count how many seconds it takes until every room is on fire.

Convert Binary Tree to Graph: Use DFS or BFS to traverse the tree. For each node:
- Create a bi-directional edge between the node and its left child (if exists).
- Create a bi-directional edge between the node and its right child (if exists).
Store these edges in an adjacency list format.
Initialize BFS: Create a que