Leetcode 99 Solution

This article provides solution to leetcode question 99 (recover-binary-search-tree)
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https://leetcode.com/problems/recover-binary-search-tree

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 {
    TreeNode* first;
    TreeNode* second;
    TreeNode* prev;

public:
    void inorder(TreeNode* root)
    {
        if (root == NULL)
            return;

        inorder(root->left);

        if (prev)
        {
            if (prev->val > root->val)
            {
                if (first == NULL)
                    first = prev;
                second = root;
            }
        }

        prev = root;

        inorder(root->right);
    }

    void recoverTree(TreeNode* root) {
        first = second = prev = NULL;

        inorder(root);

        if (first && second)
            swap(first->val, second->val);
    }
};