23. Graph BFS

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Example 1:

Input: graph = [[1, 2], [0, 3], [0, 3], [1, 2]], start = 0

Output: [0, 1, 2, 3]

Explanation: Starting from node 0, we visit its neighbors 1 and 2. Then, we visit the neighbors of 1 and 2 that haven't been visited yet, which is 3.

Example 2:

Input: graph = [[1, 2], [0], [0, 3], [2]], start = 1

Output: [1, 0, 2, 3]

Explanation: Starting from node 1, we visit its neighbor 0. Then, we visit the neighbors of 0 that haven't been visited yet (2). Finally, we visit the neighbor of 2 that hasn't been visited yet (3).

Example 3:

Input: graph = [[1], [0, 2], [1, 3], [2]], start = 3

Output: [3, 2, 1, 0]

Explanation: Starting from node 3, we visit its neighbor 2. Then, we visit the neighbors of 2 that haven't been visited yet (1). Finally, we visit the neighbor of 1 that hasn't been visited yet (0).

Constraints:

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Time Complexity

O(V+E)

Space Complexity

O(V)