# Flatten Binary Tree To Linked List Problem

## Description

LeetCode Problem 114.

Given the root of a binary tree, flatten the tree into a “linked list”:

• The “linked list” should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null.
• The “linked list” should be in the same order as a pre-order traversal of the binary tree.

Example 1:

``````1
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Input: root = [1,2,5,3,4,null,6]
Output: [1,null,2,null,3,null,4,null,5,null,6]
``````

Example 2:

``````1
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Input: root = []
Output: []
``````

Example 3:

``````1
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Input: root = 
Output: 
``````

Constraints:

• The number of nodes in the tree is in the range [0, 2000].
• -100 <= Node.val <= 100

## Sample C++ Code

``````1
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void flatten(TreeNode *root) {
while (root) {
if (root->left && root->right) {
TreeNode* t = root->left;
while (t->right)
t = t->right;
t->right = root->right;
}

if(root->left)
root->right = root->left;
root->left = NULL;
root = root->right;
}
}
``````