题目链接 : https://leetcode-cn.com/problems/convert-sorted-list-to-binary-search-tree/
题目描述:
给定一个单链表,其中的元素按升序排序,将其转换为高度平衡的二叉搜索树。
本题中,一个高度平衡二叉树是指一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过 1。
示例:
给定的有序链表: [-10, -3, 0, 5, 9],
一个可能的答案是:[0, -3, 9, -10, null, 5], 它可以表示下面这个高度平衡二叉搜索树:
0
/ -3 9
/ /
-10 5
来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/convert-sorted-list-to-binary-search-tree
著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。
思路:
与上一题108. 将有序数组转换为二叉搜索树,还是找中点
但是这个是链表找中点,所以我们用快慢指针!
代码:
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def sortedListToBST(self, head: ListNode) -> TreeNode:
def findmid(head, tail):
slow = head
fast = head
while fast != tail and fast.next!= tail :
slow = slow.next
fast = fast.next.next
return slow
def helper(head, tail):
if head == tail: return
node = findmid(head, tail)
root = TreeNode(node.val)
root.left = helper(head, node)
root.right = helper(node.next, tail)
return root
return helper(head, None)
java
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode sortedListToBST(ListNode head) {
if (head == null) return null;
return helper(head, null);
}
private TreeNode helper(ListNode head, ListNode tail) {
if (head == tail) return null;
// mid
ListNode slow = head;
ListNode fast = head;
while (fast != tail && fast.next != tail) {
slow = slow.next;
fast = fast.next.next;
}
TreeNode root = new TreeNode(slow.val);
root.left = helper(head, slow);
root.right = helper(slow.next, tail);
return root;
}
}
原文地址:https://www.cnblogs.com/powercai/p/11104608.html
时间: 2024-10-09 23:04:43