109. Convert Sorted List to Binary Search Tree - jiejackyzhang/leetcode-note GitHub Wiki

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

解题思路与108. Convert Sorted Array to Binary Search Tree类似。

首先找到中点，即是root，然后将list分成左右两部分，分别为左子树和右子树，然后用recursion完成BST的构建。

/**
 * 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; }
 * }
 */
public class Solution {
    public TreeNode sortedListToBST(ListNode head) {
        if(head == null) return null;
        ListNode slow = head;
        ListNode fast = head;
        ListNode prev = null;
        while(fast.next != null && fast.next.next != null) {
            prev = slow;
            slow = slow.next;
            fast = fast.next.next;
        }
        if(prev != null) {
            prev.next = null;
        } else {
            head = null;
        }
        TreeNode root = new TreeNode(slow.val);
        root.left = sortedListToBST(head);
        root.right = sortedListToBST(slow.next);
        return root;
    }
}