☆打卡算法☆LeetCode 109、有序链表转换二叉搜索树 算法解析

示例 1：
输入: head = [-10,-3,0,5,9]
输出: [0,-3,9,-10,null,5]
解释: 一个可能的答案是[0，-3,9，-10,null,5]，它表示所示的高度平衡的二叉搜索树。

示例 2：
输入: head = []
输出: []

class Solution {
    public TreeNode sortedListToBST(ListNode head) {
        return buildTree(head, null);
    }

    public TreeNode buildTree(ListNode left, ListNode right) {
        if (left == right) {
            return null;
        }
        ListNode mid = getMedian(left, right);
        TreeNode root = new TreeNode(mid.val);
        root.left = buildTree(left, mid);
        root.right = buildTree(mid.next, right);
        return root;
    }

    public ListNode getMedian(ListNode left, ListNode right) {
        ListNode fast = left;
        ListNode slow = left;
        while (fast != right && fast.next != right) {
            fast = fast.next;
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }
}