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 ;    }};