[LeetCode] Convert Sorted List to Binary Search Tree

Convert Sorted List to Binary Search Tree

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

解题思路：

题意为构造有序链表的二分查找树。找到中间节点的办法用双指针法。注意我们还需要保存中间节点的前一个节点，便于一个链表分成两个链表。注意滴38行，是将链表恢复成原来的模样。

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; *//** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* sortedListToBST(ListNode* head) {        if(head == NULL){            return NULL;        }        ListNode* myHead = new ListNode(0);        myHead->next = head;        ListNode* pre = myHead;        ListNode* one = head, *two = head;        while(two->next!=NULL && two->next->next!=NULL){            pre = pre->next;            one = one->next;            two = two->next->next;        }        two = one->next;        pre->next = NULL;        TreeNode* root = new TreeNode(one->val);        root->left = sortedListToBST(myHead->next);        root->right = sortedListToBST(two);        pre->next = one;    //恢复链表结构        //delete one; //这里为啥不能删除？        delete myHead;        return root;    }};