Create 0103-binary-tree-zigzag-level-order-traversal.cpp

Author: Abe0770

Diff for: cpp/0103-binary-tree-zigzag-level-order-traversal.cpp

@@ -0,0 +1,56 @@
+/*
+  Given the root of a binary tree, return the zigzag level order traversal of its nodes' values. 
+  (i.e., from left to right, then right to left for the next level and alternate between).
+
+  Ex. Input: root = [3,9,20,null,null,15,7]
+      Output: [[3],[20,9],[15,7]]
+
+  Time  : O(N)
+  Space : O(N)
+*/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
+        vector <vector <int>> v;
+        if(root == NULL)
+            return v;
+      
+        queue <TreeNode *> q;
+        q.push(root);
+        bool changeDirection = true;
+      
+        while(!q.empty()) {
+            vector <int> v1;
+            int siz = q.size();
+          
+            for(int i = 0 ; i < siz ; i++) {
+                if(changeDirection)
+                    v1.push_back(q.front() -> val);
+                else 
+                    v1.insert(v1.begin(), q.front() -> val);
+              
+                if(q.front() -> left != NULL)
+                    q.push(q.front() -> left);
+                if(q.front() -> right != NULL)
+                    q.push(q.front() -> right);
+              
+                q.pop();
+            }
+            changeDirection = !changeDirection;
+            v.push_back(v1);
+        }
+        return v;
+    }
+};