【LeetCode】Convert Sorted List to Binary Search Tree

题目

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

解答

题目要求将链表转化为二叉查找树。利用树的中序遍历的递归思想，对链表结点一个个进行访问，先对左子树进行递归，然后将当前结点作为根，迭代到下一个链表结点，最后在递归求出右子树即可

/** * 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 cur=head;        int count=0;        while(cur!=null){        cur=cur.next;        count++;        }        List<ListNode> list=new ArrayList<ListNode>();        list.add(head);        return helper(list,0,count-1);    }    private TreeNode helper(List<ListNode> list,int l,int r){    if(l>r){    return null;    }    int m=(l+r)/2;    TreeNode left=helper(list,l,m-1);  //设置左子树    TreeNode root=new TreeNode(list.get(0).val);  //设置当前节点作为根    root.left=left;    list.set(0,list.get(0).next);        root.right=helper(list,m+1,r);    return root;    }}

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