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106.cpp
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106.cpp
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/*
106. 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.
Have you met this question in a real interview?
Example
2
1->2->3 => / \
1 3
*/
/**
* Definition of ListNode
* class ListNode {
* public:
* int val;
* ListNode *next;
* ListNode(int val) {
* this->val = val;
* this->next = NULL;
* }
* }
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/
class Solution {
private:
int getCnt(ListNode* node) {
int res = 0;
while(node) {
node = node->next;
res++;
}
return res;
}
TreeNode* sortedListToBSTRecur(ListNode*& head, int beg, int end) {
if(beg > end) return NULL;
int mid = beg + (end - beg) / 2;
TreeNode* leftNode = sortedListToBSTRecur(head, beg, mid - 1);
TreeNode* root = new TreeNode(head->val);
root->left = leftNode;
head = head->next;
root->right = sortedListToBSTRecur(head, mid + 1, end);
return root;
}
public:
/**
* @param head: The first node of linked list.
* @return: a tree node
*/
TreeNode *sortedListToBST(ListNode *head) {
// write your code here
if(head == NULL) return NULL;
int cnt = getCnt(head);
return sortedListToBSTRecur(head, 0, cnt - 1);
}
};