LeetCode - Convert Sorted List to Binary Search Tree
2015-04-03 03:05
405 查看
https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/
这道题用递归很简单,每次把中间结点找到,中间结点是root,然后递归左半部份,建左子树,递归右半部份,建右子树。
找中间结点的算法就是two pointer的方法,一个每次前进一步,一个每次前进两步,知道到达tail为止。注意每次循环都需要检查 p2!=tail p2.next!=tail, 因为p2每次前进两步,如果只检查p2 != tail,可能把tail跳过了。
注意,当只有两个节点的时候,是没有左子树的,需要注意这种情况。
/article/1340712.html
这里的方法是用一边开的区间来避免找tail node和不需要保留pre指针。
这道题用递归很简单,每次把中间结点找到,中间结点是root,然后递归左半部份,建左子树,递归右半部份,建右子树。
找中间结点的算法就是two pointer的方法,一个每次前进一步,一个每次前进两步,知道到达tail为止。注意每次循环都需要检查 p2!=tail p2.next!=tail, 因为p2每次前进两步,如果只检查p2 != tail,可能把tail跳过了。
注意,当只有两个节点的时候,是没有左子树的,需要注意这种情况。
public class Solution { public TreeNode sortedListToBST(ListNode head) { if(head==null) return null; if(head.next==null){ TreeNode root = new TreeNode(head.val); return root; } ListNode tail = head; while(tail.next!=null){ tail = tail.next; } TreeNode root = getTree(head, tail); return root; } public TreeNode getTree(ListNode head, ListNode tail){ if(head==tail){ TreeNode root = new TreeNode(head.val); return root; } if(head==null||tail==null) return null; ListNode p1 = head; ListNode p2 = head; ListNode pre = head; while(p2 != tail && p2.next!=tail){ pre = p1; p1 = p1.next; p2 = p2.next.next; } TreeNode root = new TreeNode(p1.val); if(head!=p1) root.left = getTree(head, pre); root.right = getTree(p1.next, tail); return root; } }
/article/1340712.html
这里的方法是用一边开的区间来避免找tail node和不需要保留pre指针。
相关文章推荐
- [leetcode]Convert Sorted List to Binary Search Tree
- Leetcode: Convert Sorted List to Binary Search Tree
- LeetCode : Convert Sorted List to Binary Search Tree
- LeetCode-Convert Sorted List to Binary Search Tree
- [Leetcode] Convert Sorted List to Binary Search Tree
- [Leetcode]Convert Sorted List to Binary Search Tree
- [leetcode] Convert Sorted List to Binary Search Tree
- [LeetCode] Convert Sorted List to Binary Search Tree
- leetcode Convert Sorted List to Binary Search Tree
- leetcode Convert Sorted List to Binary Search Tree
- leetcode--Convert Sorted List to Binary Search Tree
- [LeetCode]Convert Sorted List to Binary Search Tree
- LeetCode: Convert Sorted List to Binary Search Tree
- LeetCode: Convert Sorted List to Binary Search Tree
- leetcode Convert Sorted List to Binary Search Tree
- LeetCode - Convert Sorted List to Binary Search Tree
- leetcode 66: Convert Sorted List to Binary Search Tree
- LeetCode_Convert Sorted List to Binary Search Tree
- [LeetCode 109] - 将已排序链表转换为二叉搜索树 (Convert Sorted List to Binary Search Tree)
- [LeetCode] Convert Sorted List to Binary Search Tree