LeetCode 114: Flatten Binary Tree to Linked List Solution

Master LeetCode problem 114 (Flatten Binary Tree to Linked List), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

114. Flatten Binary Tree to Linked List

Medium

Linked List Stack Tree Depth-First Search Binary Tree

Problem Explanation

Explanation

To flatten a binary tree into a linked list in pre-order traversal, we can follow these steps:

Recursively flatten the left subtree and right subtree.
Store the right subtree in a temporary variable.
Make the left subtree as the right subtree.
Traverse to the end of the new right subtree and attach the original right subtree.

Time Complexity: O(n) where n is the number of nodes in the binary tree. Space Complexity: O(n) due to the recursive stack.

Solution Code

class Solution {
    public void flatten(TreeNode root) {
        if (root == null) {
            return;
        }
        
        flatten(root.left);
        flatten(root.right);
        
        TreeNode temp = root.right;
        root.right = root.left;
        root.left = null;
        
        while (root.right != null) {
            root = root.right;
        }
        
        root.right = temp;
    }
}

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