【LeetCode 114】Flatten Binary Tree to Linked List (C++)

Problem:

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1
        / \
       2   5
      / \   \
     3   4   6

   1
    \
     2
      \
       3
        \
         4
          \
           5
            \
             6

Solution:

solution1:使用中序遍历思想，递归处理，关键注意pre变量

/**
 * 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:
    TreeNode* pre=NULL;
    void flatten(TreeNode* root) {
        if(root==NULL)return;
        pre=root;
        flatten(root->left);
        TreeNode* temp=root->right;
        root->right=root->left;
        root->left=NULL;
        pre->right=temp;
        flatten(temp);
    }
};

void flatten(TreeNode *root) {
	while (root) {
		if (root->left && root->right) {
			TreeNode* t = root->left;
			while (t->right)
				t = t->right;
			t->right = root->right;
		}

                if(root->left)
		    root->right = root->left;
		root->left = NULL;
		root = root->right;
	}
}