Tuesday, September 10, 2013

Recover Binary Search Tree

LeetCode

Two elements of a binary search tree (BST) are swapped by mistake.
Recover the tree without changing its structure.
Note:
A solution using O(n) space is pretty straight forward. Could you devise a constant space solution?
confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

Solution: 
Use an extra class called Pre_first_second, which is used to record the previous node of current root node, first wrong node and second wrong node, preoder-traverse the entire tree find the invalid two nodes and store hem into pre-first_sercond structure.