03. Increasing Order Search Tree.cpp

/*
Increasing Order Search Tree
============================

Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only one right child.

Example 1:
Input: root = [5,3,6,2,4,null,8,1,null,null,null,7,9]
Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

Example 2:
Input: root = [5,1,7]
Output: [1,null,5,null,7]

Constraints:
The number of nodes in the given tree will be in the range [1, 100].
0 <= Node.val <= 1000
*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

class Solution
{
  TreeNode *head, *temp;
  void inorder(TreeNode *root)
  {
    if (!root)
      return;
    inorder(root->left);
    TreeNode *newNode = new TreeNode(root->val);
    temp->right = newNode;
    temp = temp->right;
    inorder(root->right);
  }

public:
  TreeNode *increasingBST(TreeNode *root)
  {
    head = new TreeNode(-1);
    temp = head;
    inorder(root);
    return head->right;
  }
};