Leetcode: Convert Sorted List to Binary Search Tree

最新推荐文章于 2025-08-12 12:49:47 发布

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最新推荐文章于 2025-08-12 12:49:47 发布

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分类专栏： Leetcode 文章标签： leetcode

本文链接：https://blog.youkuaiyun.com/xiaoxixixiyang/article/details/40613983

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本文介绍了一种将升序排列的单链表转换为高度平衡的二叉搜索树的方法。通过类似将排序数组转换为二叉搜索树的技术，文章详细展示了如何寻找中间节点作为根节点，并递归地构建左右子树。

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

Similar method with Convert Sorted Array to Binary Search Tree.

/**
 * 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 start = head;
        ListNode end = head;
        while (end != null && end.next != null) {
            end = end.next;
        }
        return buildBST(start, end);
    }
    
    private TreeNode buildBST(ListNode start, ListNode end) {
        if (start == end) {
            return new TreeNode(start.val);
        }
        
        
        ListNode head = start;
        ListNode premid = start, mid = start;
        while (head != end && head.next != end) {
            head = head.next.next;
            premid = mid;
            mid = mid.next;
        }
        
        TreeNode node = new TreeNode(mid.val);
        if (start == mid) {
            node.left = null;
        } else {
            node.left = buildBST(start, premid);
        }
        if (mid == end) {
            node.right = null;
        } else {
            node.right = buildBST(mid.next, end);
        }
        return node;
    }
}