Symmetric Tree


Can we do it with DFS? I think it is the same as the second solution other than the fact that DFS uses stacks.
To be more specific, have two pointers(or stacks) traverse down left and right children. One will do postordertraversal on the left and the other will do preordertraversal.

There is another O(n) time O(1) space morris traversal algorithm
https://discuss.leetcode.com/topic/74692/3msciterativeontimeo1spacesolutionmorristraversal