Signed-off-by: yuduozhou <[email protected]>

Author: yuduozhou

BSTLevelOrderTraversal.java

@@ -0,0 +1,26 @@
+public class Solution {
+    public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
+        // Start typing your Java solution below
+        // DO NOT write main() function
+        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
+        if (root == null) return result;
+
+        Queue<TreeNode> nodeQ = new LinkedList<TreeNode>();
+        TreeNode dummy = new TreeNode(0);
+        nodeQ.add(root);
+        nodeQ.add(dummy);
+        while(nodeQ.size() > 0){
+            ArrayList<Integer> level = new ArrayList<Integer>();
+            while(nodeQ.peek() != dummy){
+                TreeNode temp = nodeQ.poll();
+                level.add(temp.val);
+                if (temp.left != null) nodeQ.add(temp.left);
+                if (temp.right != null) nodeQ.add(temp.right);
+            }
+            result.add(level);
+            if (nodeQ.size() == 1 && nodeQ.peek() == dummy) break;
+            nodeQ.add(nodeQ.poll());
+        }
+        return result;
+    }
+}

BSTLevelOrderZigZag.java

@@ -0,0 +1,40 @@
+/**
+ * Definition for binary tree
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public ArrayList<ArrayList<Integer>> zigzagLevelOrder(TreeNode root) {
+        // Start typing your Java solution below
+        // DO NOT write main() function
+        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
+        if (root == null) return result;
+
+        boolean backOrder = false;
+        Queue<TreeNode> nodeQ = new LinkedList<TreeNode>();
+        TreeNode dummy = new TreeNode(0);
+        nodeQ.add(root);
+        nodeQ.add(dummy);
+        while(nodeQ.size() > 0){
+            ArrayList<Integer> level = new ArrayList<Integer>();
+            while(nodeQ.peek() != dummy){
+                TreeNode temp = nodeQ.poll();
+                level.add(temp.val);
+                if (temp.left != null) nodeQ.add(temp.left);
+                if (temp.right != null) nodeQ.add(temp.right);
+            }
+            if (backOrder){
+                Collections.reverse(level);
+            }
+            result.add(level);
+            backOrder = !backOrder;
+            if (nodeQ.size() == 1 && nodeQ.peek() == dummy) break;
+            nodeQ.add(nodeQ.poll());
+        }
+        return result;
+    }
+}

README

@@ -3,8 +3,6 @@ Visiting here too often is not recommended.
 Thanks to Google, heartfire.cc, and mostly 1337code.
 
 Unfinished ones:
-Binary Tree Level Order Traversal
-Binary Tree Zigzag Level Order Traversal
 Sudoku solver
 Text Justification
 Wildcard Matching (Can't pass the large test)