897. Increasing Order Search Tree

[namespace-io]

/**
 * 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:
    TreeNode* prev;
    void inOrder(TreeNode* root){
        if(root == nullptr) return;
        inOrder(root->left);
        
        root->left = NULL;
        prev->right = root;
        prev = prev->right;
        inOrder(root->right);
    }
    
    TreeNode* increasingBST(TreeNode* root) {
        prev = new TreeNode(-1);
        auto s = prev;
        inOrder(root);
       
        return s->right;
    }
};