Flatten Binary Tree to Linked List

Flatten Binary Tree to Linked List

Total Accepted: 68105 Total Submissions: 228885 Difficulty: Medium

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

For example,
Given

         1
        / \
       2   5
      / \   \
     3   4   6

 

The flattened tree should look like:

   1
    \
     2
      \
       3
        \
         4
          \
           5
            \
             6

 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 //中序遍历的变种
class Solution {
public:
    void flatten(TreeNode* root) {
        if(!root)    return;
        
        flatten(root->left);
        
        TreeNode* tmp_right = root->right;
        
        if(root->left){
            root->right       = root->left;
            root->left        = NULL;
            while(root->right){
                root = root->right;
            }
            root->right = tmp_right;
        } 
        
        flatten(tmp_right);
    }
};

 

Next challenges: (M) Clone Graph (M) Count Univalue Subtrees (H) Closest Binary Search Tree Value II