【Leetcode】Convert Sorted List to Binary Search Tree

题目链接：https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/

题目：

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

思路：

简单起见，先把链表值存到数组中，用数组递归感觉会简单点。。

算法：

public int getListLength(ListNode head) {
int length = 0;
ListNode p = head;
while (p != null) {
length++;
p = p.next;
}
return length;
}

public TreeNode sortedListToBST(ListNode head) {
ListNode p = head;
int i = 0;
int n[] = new int[getListLength(head)];
while (p != null) {
n[i] = p.val;
i++;
p = p.next;
}
return sortedArrayToBST(n);
}

/**
* Convert Sorted Array to Binary Search Tree
*/
public TreeNode sortedArrayToBST(int[] nums) {
if (nums == null || nums.length == 0) {
return null;
}
return test(nums, 0, nums.length - 1);
}

public TreeNode test(int[] nums, int left, int right) {
if (right < left)
return null;
int mid = (left + right) / 2;
TreeNode root = new TreeNode(nums[mid]);
root.left = test(nums, left, mid - 1);
root.right = test(nums, mid + 1, right);
return root;
}