Leetcode #109 Convert Sorted List to Binary Search Tree

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

Difficulty:Medium

TreeNode* sortedListToBST(ListNode* head) {
TreeNode* root;
if(head==NULL)
return NULL;
if(head->next==NULL)
{
root = new TreeNode(head->val);
return root;
}
ListNode* p = head;
ListNode* pNext = p;
ListNode* pre = p;
while(pNext->next!=NULL&&pNext->next->next!=NULL){
pre = p;
p = p->next;
pNext = pNext->next->next;
}
root = new TreeNode(p->val);
p = p->next;
pre->next = NULL;
if(root->val == head->val)
head = NULL;
root->left = sortedListToBST(head);
root->right = sortedListToBST(p);

return root;
}