114. 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

click to show hints.

Hints:

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

题意：将一颗树变成平展的类型。

思路：对根结点处理时，将根的左子树挪为根的右子树，跟的右子树接到左子树的最右子树的右边的结点（这样确保右子树在所有左子树都访问完会访问到）。

/** * 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 flatten(TreeNode* root) {if (root == NULL)return;TreeNode* left = root->left;TreeNode* right = root->right;if (left != NULL){root->left = NULL;root->right = left;TreeNode* tmp = left;while (tmp->right){tmp = tmp->right;}tmp->right = right;}flatten(root->right);}};