add zigzagLevelOrder traversal in binary tree (#14)

Author: naveenkash

Diff for: JavaScript/Binary-Tree-ZigZag-Traversal.js

@@ -0,0 +1,59 @@
+/**
+* Binary Tree ZigZag level Order Traversal
+* Medium
+* 
+
+Example 1:
+
+Given a binary tree, return the zigzag level order traversal of its nodes' values.
+(ie, from left to right, then right to left for the next level and alternate between).
+
+For example:
+Given binary tree [3,9,20,null,null,15,7],
+
+    3
+   / \
+  9  20
+    /  \
+   15   7
+
+return its zigzag level order traversal as:
+
+[
+  [3],
+  [20,9],
+  [15,7]
+]
+
+* Logic : Using Breadth First Search to Solve This Problem.
+          Using a boolean to push in front of array and in end of the array and toogle it after every level traversed
+* Runtime: 80 ms
+* Memory Usage: 37.6 MB
+*
+*/
+
+var zigzagLevelOrder = function (root) {
+  let queue = [],
+    result = [],
+    zigzag = true;
+  if (root == null) return [];
+  queue.push(root);
+  while (queue.length) {
+    let size = queue.length;
+    let temp = [];
+    while (size--) {
+      let pop = queue.shift();
+      if (pop && pop.left) queue.push(pop.left);
+      if (pop && pop.right) queue.push(pop.right);
+      if (zigzag) {
+        if (pop) temp.push(pop.val);
+      } else {
+        if (pop) temp.unshift(pop.val);
+      }
+    }
+    zigzag = !zigzag;
+    result.push(temp);
+  }
+
+  return result;
+};

Diff for: README.md

@@ -123,6 +123,18 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 </div>
 <br/>
 
+## Tree
+
+| #   | Title                                                                 | Solution                                  | Time   | Space  | Difficulty | Tag   | Note |
+| --- | --------------------------------------------------------------------- | ----------------------------------------- | ------ | ------ | ---------- | ----- | ---- |
+| 103 | [ZigZag Level Order](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/) | [JavaScript](./JavaScript/Binary-Tree-ZigZag-Traversal.js) | _O(n)_ | _O(n)_ | Medium       | Binary Tree |      |
+
+<br/>
+<div align="right">
+    <b><a href="#algorithms">⬆️ Back to Top</a></b>
+</div>
+<br/>
+
 ## Hash Table
 
 | #   | Title                                                         | Solution                          | Time   | Space  | Difficulty | Tag | Note          |