leetcode_question_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

Hints:

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

void flatten(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root==NULL) return;
        if(root->left == NULL && root->right == NULL) return;
		flatten(root->left);
		flatten(root->right);

		TreeNode* tmpright = root->right;
		root->right = root->left;
		root->left = NULL;
		TreeNode* tmp = root;
		while(tmp->right)
			tmp = tmp->right;
		tmp->right = tmpright;
        return;
    }