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897. Increasing Order Search Tree

EasyOpen on LeetCodeProblem statement

Problem Statement

897. Increasing Order Search Tree

Easy

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:

C++

Source file
/**
 * 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 {
public: 
    TreeNode* increasingBST(TreeNode* ptr) {
        auto ltToken = ptr;
        if (ptr){
            // cout << "\n#" << ptr->val;
            if (ptr->right){
                ptr->right = increasingBST(ptr->right);
                
            }
            if (ptr->left){
                ltToken = ptr->left;
                while(ltToken->left)
                    ltToken=ltToken->left;
                increasingBST(ptr->left);
                if (ptr->left->right){
                    auto s = ptr->left->right;
                    while (s->right)
                        s = s->right;
                    s->right = ptr;
                }
                else ptr->left->right = ptr;
                ptr->left = nullptr;
            }
        }
        return (ltToken ? ltToken : ptr);
    }
};