从上到下打印出二叉树的每个节点,同一层的节点按照从左到右的顺序打印。
例如:
给定二叉树: [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回:
[3,9,20,15,7]
提示:
节点总数 <= 1000
代码:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int[] levelOrder(TreeNode root) {
List<Integer> list = new ArrayList<Integer>();
Queue<TreeNode> queue = new LinkedList<>();
if(root==null) return new int[]{};
queue.offer(root);
while(!queue.isEmpty())
{
TreeNode p = queue.poll();
list.add(p.val);
if(p.left!=null)
{
queue.offer(p.left);
}
if(p.right!=null)
{
queue.offer(p.right);
}
}
int[] res = new int[list.size()];
for(int i=0; i<res.length; i++) {
res[i] = list.get(i);
}
return res;
}
}