[110]Convert Sorted List to Binary Search Tree

【题目描述】

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

【思路】

基本上和 Convert
Sorted Array to Binary Search Tree这道题的类似，不过因为是列表，所以需要通过遍历的方法来查找中间结点。

【代码】

/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* sortedListToBST(ListNode* head) {
int len=0;
ListNode* node=head;
while(node){
len++;
node=node->next;
}
return convert(head,len);
}
TreeNode* convert(ListNode* node,int cnt){
if(node==NULL||cnt==0) return NULL;
if(cnt==1) return new TreeNode(node->val);
int mid=cnt%2==0?cnt/2-1:cnt/2;
ListNode* p=node;
for(int i=0;i<mid;i++){
p=p->next;
}
TreeNode* parent=new TreeNode(p->val);
parent->left=convert(node,mid);
parent->right=convert(p->next,cnt/2);
return parent;
}
};