Update 二叉树相关.md

blogs/Algorithm/剑指 Offer/二叉树相关.md

@@ -133,3 +133,35 @@ class Solution {
 }
 ```
 
+#### [32 - I. 从上到下打印二叉树](https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/)
+
+```java
+class Solution {
+
+    public int[] levelOrder(TreeNode root) {
+        if (root == null) {
+            return new int[0];
+        }
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.add(root);
+        List<Integer> list = new ArrayList<>();
+        while (!queue.isEmpty()) {
+            TreeNode node = queue.poll();
+            list.add(node.val);
+            if (node.left != null) {
+                queue.add(node.left);
+            }
+            if (node.right != null) {
+                queue.add(node.right);
+            }
+        }
+        int[] result = new int[list.size()];
+        int index = 0;
+        for (int i : list) {
+            result[index++] = i;
+        }
+        return result;
+    }
+}
+```
+