[leetcode] 897. Increasing Order Search Tree

/**
 * 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* answer = new TreeNode(-1);
    TreeNode* dummy = answer;
    TreeNode* increasingBST(TreeNode* root) {
        if(!root) return nullptr;
        
        increasingBST(root->left);
        
        TreeNode* tmp = new TreeNode(root->val);
        answer->right = tmp;
        answer = answer->right;
        
        increasingBST(root->right);
        
        return dummy->right;
    }
};

 

Inorder Traversal을 쭉 돌리면 되는 간단한 문제

시간복잡도: O(n)