【LeetCode】Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

思路一：先将链表转换成数组，再用之前的算法。

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode *sortedListToBST(ListNode *head) {
vector<int> num;
while(NULL != head){
num.push_back(head->val);
head = head->next;
}
int N = num.size();
return sortedArrayToBSTRe(num,0,N-1);
}
TreeNode *sortedArrayToBSTRe(vector<int> &num, int begin, int end){
if(begin > end)return NULL;
int pos = (begin + end)/2;
TreeNode* root = new TreeNode(num[pos]);
root->left = sortedArrayToBSTRe(num,begin,pos-1);
root->right = sortedArrayToBSTRe(num,pos+1,end);
return root;
}
};