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Convert_Sorted_List_to_Binary_Search_Tree.cpp
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Convert_Sorted_List_to_Binary_Search_Tree.cpp
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode *sortedListToBSTUtils(ListNode *head) {
if(head == nullptr) {
return nullptr;
}
ListNode *slow = head, *fast = head->next;
ListNode *tail = nullptr;
while(fast and fast->next) {
fast = fast->next;
tail = slow;
slow = slow->next;
if(fast) fast = fast->next;
}
ListNode *middle = slow;
// gotcha
if(tail) tail->next = nullptr;
if(head == middle) head = nullptr;
TreeNode *node = new TreeNode(middle->val);
node->left = sortedListToBSTUtils(head);
node->right = sortedListToBSTUtils(middle->next);
return node;
}
TreeNode *sortedListToBST(ListNode *head) {
return sortedListToBSTUtils(head);
}
};