二叉树层序遍历
size
表示当前这一层的节点个数- 一次
while
就会遍历一层
public ... travel(TreeNode root) {
...
Deque<TreeNode> queue = new ArrayDeque();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
for (int i = 0; i < size; i++) {
node = queue.poll();
if (node.left != null) queue.offer(node.left);
if (node.right != null) queue.offer(node.right);
}
...
}
return ...;
}