[LeetCode-114] 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

 

 

前序历遍的变形吧。

 

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (NULL == root) {
            return;
        }
        bool is_flatten = false;
        TreeNode *pnext = NULL, *pnode = NULL, *pright = NULL;
        while (!is_flatten) {
            pnode = pnext = root;
            is_flatten = true;
            while (NULL != pnext->left || NULL != pnext->right) {
                if (NULL != pnext->left) {
                    is_flatten = false;
                    pnode = pnext;
                    pnext = pnext->left;
                } else {
                    pnext = pnext->right;
                }
            }
            if (!is_flatten) {
                pright = pnode->right;
                pnode->right = pnode->left;
                pnode->left = NULL;
                while (NULL != pnode->right) {
                    pnode = pnode->right;
                }
                pnode->right = pright;
            }
        }  
    }  
};