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;
}