Binary Tree BFS/DFS Traversal

Given a binary tree, implement three traversal methods:

1. Breadth-First Search (BFS) - level order traversal
2. Depth-First Search (DFS) - recursive preorder
3. Depth-First Search (DFS) - iterative preorder using a stack

Return the order of visited nodes for each traversal.

Constraints:

• 0 <= number of nodes <= 10^4
• -100 <= Node.val <= 100

Example 1: ` Input: root = [1,2,3,4,5,6,7] 1 /
2 3 / \ /
4 5 6 7

Output:

• BFS: [1, 2, 3, 4, 5, 6, 7]
• DFS Recursive: [1, 2, 4, 5, 3, 6, 7]
• DFS Iterative: [1, 2, 4, 5, 3, 6, 7] `

Example 2: Input: root = [1] Output: [1] for all methods

Example 3: Input: root = [] Output: [] for all methods

Source: Apple Phone Screen