Convert Sorted List to Binary Search Tree

最新推荐文章于 2020-04-13 06:45:19 发布

dutsoft

最新推荐文章于 2020-04-13 06:45:19 发布

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文章标签：数据结构二叉树链表

本文链接：https://blog.youkuaiyun.com/dutsoft/article/details/38703369

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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。通过快慢指针找到中点作为根节点，并递归地构造左右子树。

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

/**
 * 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) {
        return constructBST(head);
    }
    public TreeNode constructBST(ListNode head){
        if(head==null) return null;
        if(head.next==null) return new TreeNode(head.val);
        ListNode fast=head;
        ListNode slow=head;
        ListNode prev=null;
        while(fast!=null && fast.next!=null){
            fast=fast.next.next;
            prev=slow;
            slow=slow.next;
        }
        if(prev!=null) prev.next=null;
        TreeNode tree=new TreeNode(slow.val);
        tree.left=constructBST(head);
        tree.right=constructBST(slow.next);
        return tree;
    }
}