LeetCode[102]. Level Order Traversal of Binary Tree

For regular traversal, you can simply use a queue. Note the creation and usage of the Java queue.

[!NOTE]
The creation of a Java queue is generally done using LinkedList, for example, Queue<TreeNode> q = new LinkedList<>();

add() and offer() are used to add elements to the end of the queue; offer() is safer, while add() will throw an exception if the queue is full.

poll() removes and returns the head element of the queue, equivalent to combining C++'s front() and pop().

peek() returns the head element of the queue but does not remove it.

size() returns the number of elements in the queue; isEmpty() checks if the queue is empty.

contains(Object o) checks if the queue contains a specific element.

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