feat(leetcode): add No.107

Author: mickey0524

107.Binary-Tree-Level-Order-Traversal-II.java

@@ -0,0 +1,52 @@
+// https://leetcode.com/problems/binary-tree-level-order-traversal-ii/
+//
+// algorithms
+// Easy (47.04%)
+// Total Accepted: 229,826
+// Total Submissions: 488,538
+// beats 100.0% of java submissions
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public List<List<Integer>> levelOrderBottom(TreeNode root) {
+        LinkedList<List<Integer>> res = new LinkedList<>();
+        if (root == null) {
+            return res;
+        }
+        
+        LinkedList<TreeNode> q = new LinkedList<>();
+        ArrayList<Integer> path = new ArrayList<>();
+        q.add(root);
+        q.add(null);
+        
+        while (true) {
+            TreeNode curItem = q.pollFirst();
+            if (curItem == null) {
+                res.offerFirst(new ArrayList<Integer>(path));
+                if (q.size() == 0) {
+                    break;
+                }
+                path.clear();
+                q.add(null);
+            } else {
+                path.add(curItem.val);
+                if (curItem.left != null) {
+                    q.add(curItem.left);
+                }
+                if (curItem.right != null) {
+                    q.add(curItem.right);
+                }
+            }
+        }
+        
+        return res;
+    }
+}