Learned a lot for today's mock interview

Author: zhongn2

Diff for: Binary Tree Zigzag Level Order Traversal.cpp

@@ -0,0 +1,39 @@
+// set a boolean flag to control the order
+
+
+class Solution {
+public:
+    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
+        vector<vector<int> > result;
+        if(!root) return result;
+        
+        queue<TreeNode *> curr;
+        vector<int> level;
+        bool ordered = true;
+        curr.push(root);
+        curr.push(NULL); // NULL seperator between levels
+        
+        while(!curr.empty()){
+            TreeNode *head = curr.front();
+            curr.pop();
+            if(head){
+                level.push_back(head ->val);
+                if(head -> left) curr.push(head -> left);
+                if(head -> right) curr.push(head -> right);
+            }else{ // decide the order
+                if(ordered){
+                    result.push_back(level);
+                }else{
+                    reverse(level.begin(), level.end());
+                    result.push_back(level);
+                }
+                level.clear();
+                ordered = ! ordered;
+                if(curr.size() > 0) curr.push(NULL);
+            }
+        }
+        
+    return result;
+       
+    }
+};