[LeetCode] 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

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode *root) {
        if(root==NULL)
            return;
        TreeNode *p = root;
        Recur(p);
    }
private:
    void Recur(TreeNode *p){
        if(p==NULL)
            return;
        TreeNode *pleft=p->left;
        TreeNode *pright = p->right;
        p->left = NULL;
        p->right = pleft;
        Recur(pleft);
        while(pleft){//找到pleft的最末点
           p = pleft;
           pleft = pleft->right;
        }
        p->right = pright;
        Recur(pright);
    }
};