114. Flatten Binary Tree to Linked List

https://leetcode.com/problems/flatten-binary-tree-to-linked-list/

Problem

Given a binary tree, flatten it to a linked list in-place.

For example, given the following tree:

    1
   / \
  2   5
 / \   \
3   4   6

The flattened tree should look like:

1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6

Solution

/**
 * 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) {
        if (!root) return;
        flatten(root->left);
        flatten(root->right);
        if (!root->left) return;
        auto *leftright = getRightMostNode(root->left);
        leftright->right = root->right;
        root->right = root->left;
        root->left = nullptr;
    }
    inline TreeNode* getRightMostNode(TreeNode* root) {
        if (!root) return root;
        while (root->right) root = root->right;
        return root;
    }
    
};

• #tree

• #dfs