---
tags: leetcode
---

# [114. Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)
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# My Solution
## The Key Idea for Solving This Coding Question
Use Morris traversal to solve this coding question.
## C++ Code

/**
 * 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:
    void flatten(TreeNode *root) {
        while (root != nullptr) {
            if (root->left != nullptr) {
                TreeNode *x = root->left;
                while (x->right != nullptr) {
                    x = x->right;
                }

                x->right = root->right;
                root->right = root->left;
                root->left = nullptr;
                root = root->right;
            } else {
                root = root->right;
            }
        }
    }
};

### Time Complexity
$O(n)$
* $n$ is the number of nodes in the binary tree.
### Space Complexity
$O(1)$
# Miscellaneous
<!--
# Test Cases

[1,2,5,3,4,null,6]

[]

[0]

[5,4,8,11,null,13,4,7,2,null,null,5,1]

[5,4,8,11,null,13,4,7,2,null,null,null,1]

[1,2]

[1,null,2]

[-2,6,null,0,-6]

-->