题目：给出一个所有元素以升序排序的单链表，将它转换成一棵高度平衡的二分查找树
思路：每次取一个中间元素，递归。
class Solution {
public:/*
* @param head: The first node of linked list.
* @return: a tree node
*/
TreeNode * func(int left,int right,vector<int> arr){
if(right<left) return NULL;//? <=
int mid=(left+right)/2;
TreeNode *tree = new TreeNode(arr[mid]);
tree->left=func(left,mid-1,arr);
tree->right=func(mid+1,right,arr);
return tree;
}
TreeNode * sortedListToBST(ListNode * head) {
if(head==NULL) return NULL;
vector<int> arr;
ListNode *p=head;
while(p!=NULL){
arr.push_back(p->val);
p=p->next;
}
return func(0,arr.size()-1,arr);
// write your code here
}
};
ps:树那里都要忘得差不多了 每天一道lintcode 捡起来