:

 Write an algorithm to do spiral order traversal of binary tree?

In level order traversal we make use of a single queue while in spiral order traversal we need use two stacks.

Nodes at even level are stored in 'stackEven' and are pushed in it from left to right order whereas nodes at odd level are stored in 'stackOdd' and are pushed in it from right to left order.

Algorithm:

1. Push root node into the 'stackEven'. Set boolean 'evenLevel' to true. This boolean variable is used to indicate if the current level being visited is even level or odd level.

2. Now if 'evenLevel' is set to true repeat steps 2a to 2c until 'stackEven' is not empty.

2a. Pop the node from 'stackEven'. Let popped node be 'currentNode'. Print the value of 'currentNode'.

2b. If the right child of 'currentNode' is not null, push it into the 'stackOdd'.

2c. If the left child of 'currentNode' is not null, push it into the 'stackOdd'.

3. If 'evenLevel' is not set to true then repeat steps 3a to 3c until 'stackOdd' is not empty.

3a. Pop the node from 'stackOdd'. Let popped node be 'currentNode'. Print the value of 'currentNode'.

3b. If the left child of 'currentNode' is not null, push it into the 'stackEven'.

3c. If the right child of 'currentNode' is not null, push it into the 'stackEven'.

4. If 'evenLevel' is true set it to false and if it is false set it to true. This is because the next level visited would be odd if current level is even and vice versa.

5. Repeat steps 2-4 until both 'stackEven' and 'stackOdd' are not empty.

Implementation details could be found in function 'spiralTraversal(TreeNode root)' in the code snippet.

Example: Let's look at the state of the stacks as nodes in each level are visited for the following tree.

The time complexity of this algorithm is O(n) and extra space used is also O(n).

a  social news website  is an  internet  website  that features  user-posted stories. such stories are ranked based on popularity, as voted on by other users of the site or by website administrators. users typically comment online on the news posts and these comments may also be ranked in popularity. since their emergence with the birth of  web 2.0, social news sites have been used to link many types of information, including news, humor, support, and discussion. all such websites allow the users to submit content and each site differs in how the content is moderated. on the  slashdot  and  fark  websites,  administrators  decide which articles are selected for the front page. on  reddit  and  digg, the articles that get the most votes from the community of users will make it to the front page. many social news websites also feature an online comment system, where users discuss the issues raised in an article. some of these sites have also applied their voting system to the comments, so that the most popular comments are displayed first. some social news websites also have a  social networking  function, in that users can set up a user profile and follow other users' online activity on the website.