LeetCode-convert-sorted-list-to-binary-search-tree

题目描述

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

把一个有序链表转化为平衡二叉树。

思路：利用快慢指针找到中间节点，这也就是根节点，然后递归调用生成平衡二叉树函数分别生成根节点的左右节点。

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; next = null; } * } *//** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public TreeNode sortedListToBST(ListNode head) {        if(head == null)            return null;                ListNode fast = head;        ListNode slow = head;        ListNode temp = null;        while(fast != null && fast.next != null) {            fast = fast.next.next;            temp = slow;            slow = slow.next;        }        if(temp == null)        {            head = null;        }else{            temp.next = null;        }        //上面几行代码必须加，不加报索引越界错误。        TreeNode root = new TreeNode(slow.val);                root.left = sortedListToBST(head);        root.right = sortedListToBST(slow.next);                return root;    }}