main2.cpp

/// Source : https://leetcode.com/problems/increasing-order-search-tree/description/
/// Author : liuyubobobo
/// Time   : 2018-09-01

#include <iostream>
#include <vector>

using namespace std;

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


/// Inorder traversal and link during the traversal
/// Time Complexity: O(n)
/// Space Complexity: O(h) where h is the height of the tree
class Solution {
public:
    TreeNode* increasingBST(TreeNode* root) {

        if(root == NULL)
            return NULL;

        TreeNode* tail;
        return inOrder(root, tail);
    }

private:
    TreeNode* inOrder(TreeNode* node, TreeNode* &tail){

        if(node->left == NULL && node->right == NULL){
            tail = node;
            return node;
        }

        TreeNode* ret;
        if(node->left){
            ret = inOrder(node->left, tail);
            tail->left = NULL;
            tail->right = node;
        }
        else
            ret = node;

        node->left = NULL;
        tail = node;
        if(node->right) {
            TreeNode *root = inOrder(node->right, tail);
            node->right = root;
        }

        return ret;
    }
};


int main() {

    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    Solution().increasingBST(root);

    return 0;
}