LeetCode-- Flatten Binary Tree to Linked List

Flatten Binary Tree to Linked List

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

这个道题方法有多种，虽然下面这个很简单，但我觉得还是蛮经典。

C++代码：

class Solution {
public:
    void flatten(TreeNode* root) {
        if(!root) return;

        flatten(root->left);
        flatten(root->right);

        if (nullptr == root->left) return;

        TreeNode *p=root->left;
        while(p->right) p=p->right;
        p->right = root->right;
        root->right = root->left;
        root->left = nullptr;
    }
};