https://blog.csdn.net/XTAOTWO/article/details/83625586
广度优先遍历
public List<Integer> bfs(TreeNode root) {
Queue<TreeNode> queue = new LinkedList<TreeNode>();
List<Integer> list = new LinkedList<Integer>();
if (root == null) {
return list;
}
queue.add(root);
while (!queue.isEmpty()) {
TreeNode treeNode = queue.remove();
if (null != treeNode.leftNode) {
queue.add(treeNode.leftNode);
}
if (null != treeNode.rightNode) {
queue.add(treeNode.rightNode);
}
list.add(treeNode.val);
}
return list;
}