有了上面的教训,这道题就简单多了,什么时候该更新pre是明白的了,倒是有个细节,二叉搜索树中是不同意有相等节点的,所以题目的要求用黑体字标明了.写的时候注意就能够了. class Solution { public: TreeNode *pre = NULL; bool isValidBST(TreeNode *root) { if(root == NULL) return true; bool res = true; if(root->left) res &= isValidBST(roo…

这道题事实上跟二叉搜索树没有什么关系,给定n个节点,让你求有多少棵二叉树也是全然一样的做法.思想是什么呢,给定一个节点数x.求f(x),f(x)跟什么有关系呢,当然是跟他的左右子树都有关系.所以能够利用其左右子树的结论.大问题被成功转化成了小问题.最熟悉的方法是递归和dp.这里显然有大量的反复计算.用dp打表好一些. 后来实验的同学说,这事实上是一个Catalan数,上网查了一下,果然啊.Catalan数是这样子的: h(0) = 1, h(1) = 1; 递推式:h(n)= h(0)*h(n-…

[LeetCode]99. Recover Binary Search Tree 解题报告(Python) 标签(空格分隔): LeetCode 题目地址:https://leetcode.com/problems/recover-binary-search-tree/description/ 题目描述: Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without chan…

Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST. Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than or equal to the nod…

一天一道LeetCode 本系列文章已全部上传至我的github,地址:ZeeCoder's Github 欢迎大家关注我的新浪微博,我的新浪微博 欢迎转载,转载请注明出处 (一)题目 Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. Note: A solution using O(n) space is pret…

原题链接在这里:https://leetcode.com/problems/find-mode-in-binary-search-tree/#/description 题目: Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST. Assume a BST is defined as follows…

Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. 来源:力扣(LeetCode)链接:https://leetcode-cn.com/problems/recover-binary-search-tree著作权归领扣网络所有.商业转载请联系官方授权,非商业转载请注明出处. [题意分析] 对于一个BST应该了解的一个重…

作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 目录 题目描述 题目大意 解题方法 递归 日期 题目地址:https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal/ 题目描述 Return the root node of a binary search tree that matches the given preorder…

题目链接:Recover Binary Search Tree | LeetCode OJ Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. Note: A solution using O(n) space is pretty straight forward. Could you devise a constan…

题目链接:Validate Binary Search Tree | LeetCode OJ Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right…