solve binary tree level order traversal

Author: sora0319

binary-tree-level-order-traversal/sora0319.java

@@ -0,0 +1,26 @@
+class Solution {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        if (root == null) return new ArrayList<>();
+
+        List<List<Integer>> output = new ArrayList<>();
+        Queue<TreeNode> q = new LinkedList<>();
+        q.offer(root);
+
+        while (!q.isEmpty()) {
+            List<Integer> values = new ArrayList<>();
+            int size = q.size();
+
+            for (int i = 0; i < size; i++) {
+                TreeNode node = q.poll();
+                values.add(node.val);
+
+                if (node.left != null) q.offer(node.left);
+                if (node.right != null) q.offer(node.right);
+            }
+
+            output.add(values);
+        }
+
+        return output;
+    }
+}