Leetcode 99. Recover Binary Search Tree (Hard) (cpp)

Leetcode 99. Recover Binary Search Tree (Hard) (cpp)

Tag: Tree, Depth-first Search

Difficulty: Hard

/*99. Recover Binary Search Tree (Hard)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?*//*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}* };*/class Solution {public:void recoverTree(TreeNode* root) {TreeNode* first = NULL, *second = NULL, *pre = new TreeNode(INT_MIN);inOrder(root, first, second, pre);swap(first->val, second->val);return;}private:void inOrder(TreeNode* root, TreeNode*& first, TreeNode*& second, TreeNode*& pre) {if (root == NULL) {return;}inOrder(root->left, first, second, pre);if (pre->val >= root->val) {if (first == NULL) {first = pre;}if (first != NULL) {second = root;}}pre = root;inOrder(root->right, first, second, pre);}};