使用队列代码
从上往下打印二叉树
http://www.nowcoder.com/questionTerminal/7fe2212963db4790b57431d9ed259701
public class Solution {
public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
LinkedList<TreeNode> queue = new LinkedList<>();
ArrayList<Integer> result = new ArrayList<>();
queue.add(root);
while(!queue.isEmpty()) {
TreeNode node = queue.poll();
if(node != null) {
result.add(node.val);
queue.add(node.left);
queue.add(node.right);
}
}
return result;
}
} 
查看16道真题和解析