Leetcode-114: expand binary tree into linked list

subject

Topic linking
Give you the root node of the binary tree root , Please expand it into a single linked list ：

The expanded single linked list should also be used TreeNode , among right The child pointer points to the next node in the list , The left sub pointer is always null .
The expanded single linked list should be the same as the binary tree The first sequence traversal Same order .

Example 1：

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

Example 2：

 Input ：root = []
 Output ：[]

Example 3：

 Input ：root = [0]
 Output ：[0]

Problem solving

Method 1 ：

Reference link

class Solution {
    
public:
    void flatten(TreeNode* root) {
    
        while(root){
    
            TreeNode* p=root->left;
            if(p){
    
                while(p->right) p=p->right;
                p->right=root->right;
                root->right=root->left;
                root->left=nullptr;
            }
            root=root->right;
        }
    }
};