## Convert Sorted List to Binary Search Tree

### 描述

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

### 分治法，自顶向下

// Convert Sorted List to Binary Search Tree
// 二分法，类似于 Convert Sorted Array to Binary Search Tree，
// 自顶向下，时间复杂度O(nlogn)，空间复杂度O(logn)
class Solution {
public:

TreeNode *root = new TreeNode(mid->val);
root->right = sortedListToBST(mid->next);

return root;
}

while(fast != nullptr && fast->next != nullptr){
prev_slow = slow;
slow = slow->next;
fast = fast->next->next;
}

prev_slow->next = nullptr;
return slow;
}
};

### 自底向上

// Convert Sorted List to Binary Search Tree
// bottom-up，时间复杂度O(n)，空间复杂度O(logn)
class Solution {
public:
int len = 0;
while (p) {
len++;
p = p->next;
}
return sortedListToBST(head, 0, len - 1);
}
private:
TreeNode* sortedListToBST(ListNode*& list, int start, int end) {
if (start > end) return nullptr;

int mid = start + (end - start) / 2;
TreeNode *leftChild = sortedListToBST(list, start, mid - 1);
TreeNode *parent = new TreeNode(list->val);
parent->left = leftChild;
list = list->next;
parent->right = sortedListToBST(list, mid + 1, end);
return parent;
}
};