Convert Sorted List to Binary Search Tree

一、概述

平衡二叉树是一颗n个节点的高度为lgn的二叉查找树，严格维持节点的左右节点数差的绝对值小于等于1

对于一个已经排好序的链表来说，只需要找到中间点，把其当做root，其左边链表为root的left节点，其右边链表为root的right节点，递归构造就行

二、代码

struct ListNode {    int val;    ListNode *next;    ListNode(int x) : val(x), next(NULL) {}};struct TreeNode {    int val;    TreeNode *left;    TreeNode *right;    TreeNode(int x) : val(x), left(NULL), right(NULL) {}};class Solution {public:    TreeNode* sortedListToBST(ListNode* head) {        TreeNode *root = NULL;        if (head != NULL) {            ListNode *slow, *fast, *pre;            slow = fast = head;            pre = NULL;            while (fast->next && fast->next->next) {                pre = slow;                slow = slow->next;                fast = fast->next->next;            }            if (pre != NULL) pre->next = NULL;            else head = NULL;            root = new TreeNode(slow->val);            root->left = sortedListToBST(head);            root->right = sortedListToBST(slow->next);        }        return root;    }};