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

解析:

变换后的链表是按照先序遍历的顺序，只需要把左子树变成链表，然后链表的最后节点指向右子树的链表，把根节点右子树指向左子树链表，左子树置空即可。

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:

    void flat(TreeNode* root)
    {
        if (root==NULL) return ;
        if (root->left==NULL &&root->right==NULL) return ;
        TreeNode *leftroot=root->left;
        TreeNode *rightroot=root->right;
        if (root->left)
        {
            flat(leftroot);
        }
        if (root->right)
        {
            flat(rightroot);
        }
        if (leftroot!=NULL)
        {
             TreeNode* temp=leftroot;
            while(leftroot->right)
            {
                leftroot=leftroot->right;
            }
            leftroot->right=rightroot;
             root->right=temp;
            root->left=NULL;
        }
       
        return ;
    }

    void flatten(TreeNode* root) {
        flat(root);
        return ;
    }
};