solves #103 in java

Author: anishLearnsToCode

Diff for: README.md

@@ -95,7 +95,7 @@
 | 100  | [Same Tree](https://leetcode.com/problems/same-tree)                                                                                                      |                                          [![Java](assets/java.png)](src/SameTree.java) [![Python](assets/python.png)](python/same_tree.py)                                           |                                                                                                                                   |
 | 101  | [Symmetric Tree](https://leetcode.com/problems/symmetric-tree)                                                                                            |                                     [![Java](assets/java.png)](src/SymmetricTree.java) [![Python](assets/python.png)](python/symmetric_tree.py)                                      |                                                                                                                                   |
 | 102  | [Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal)                                                      |                                                          [![Java](assets/java.png)](src/BinaryTreeLevelOrderTraversal.java)                                                          |                                                                                                                                   |
-| 103  | [Binary Tree Zigzag Level Order Traversal](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal)                                        |                                                                                                                                                                                      |                                                                                                                                   |
+| 103  | [Binary Tree Zigzag Level Order Traversal](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal)                                        |                                                       [![Java](assets/java.png)](src/BinaryTreeZigzagLevelOrderTraversal.java)                                                       |                                                                                                                                   |
 | 104  | [Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree)                                                                |                         [![Java](assets/java.png)](src/MaximumDepthOfBinaryTree.java) [![Python](assets/python.png)](python/maximum_depth_of_binary_tree.py)                         |                                                                                                                                   |
 | 105  | [Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal)      |                                                                                                                                                                                      |                                                                                                                                   |
 | 106  | [Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal)    |                                                                                                                                                                                      |                                                                                                                                   |

Diff for: src/BinaryTreeZigzagLevelOrderTraversal.java

@@ -0,0 +1,50 @@
+// https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal
+// T: O(n)
+// S: O(n)
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+public class BinaryTreeZigzagLevelOrderTraversal {
+    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
+        if (root == null) return Collections.EMPTY_LIST;
+
+        final List<List<Integer>> result = new ArrayList<>();
+        final Queue<TreeNode> queue = new LinkedList<>();
+        queue.add(root);
+        queue.add(null);
+
+        List<Integer> level = new ArrayList<>();
+
+        while (!queue.isEmpty()) {
+            final TreeNode current = queue.poll();
+            if (current == null) {
+                result.add(level);
+                level = new LinkedList<>();
+                if (!queue.isEmpty()) {
+                    queue.add(null);
+                }
+                continue;
+            }
+            level.add(current.val);
+            addChildrenInQueue(queue, current);
+        }
+
+        zigZagOrder(result);
+        return result;
+    }
+
+    private void zigZagOrder(List<List<Integer>> levels) {
+        for (int i = 1 ; i < levels.size() ; i += 2) {
+            Collections.reverse(levels.get(i));
+        }
+    }
+
+    private void addChildrenInQueue(Queue<TreeNode> queue, TreeNode root) {
+        if (root.left != null) queue.add(root.left);
+        if (root.right != null) queue.add(root.right);
+    }
+}

Diff for: src/HelloWorld.java

@@ -1,11 +1,10 @@
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
 public class HelloWorld {
     public static void main(String[] args) {
-        Trie trie = new Trie();
-        trie.insert("apple");
-//        System.out.println(trie.search("apple"));
-//        System.out.println(trie.search("app"));
-        System.out.println(trie.startsWith("app")); // true
-        trie.insert("app");
-//        System.out.println(trie.search("app"));
+        List<Integer> list = new ArrayList<>();
+        Collections.reverse(list);
     }
 }