原题链接 题意简介 要求有多少种 n 的排列,能够通过二分法正确地找到放在 pos 处的数字 x. 答案对 1e9+7 取模.n<=1000. 采用的二分法如下图: 思路分析 首先,这个排列中有一个位置是固定的,就是 a[pos] = x . 我们知道,二分查找的过程是不断缩小区间的过程,想要找到一个已经确定放在 pos 位置上的 x ,需要判断的 mid 的位置,需要的大于 x 的数的个数 c1 和小于 x 的数的个数 c0 也是固定的. 也就是说,我们只需要模拟这个二分过程,求解出 c0 和…

Binary Search基础 应用于已排序的数据查找其中特定值,是折半查找最常的应用场景.相比线性查找(Linear Search),其时间复杂度减少到O(lgn).算法基本框架如下: //704. Binary Search int search(vector<int>& nums, int target) { //nums为已排序数组 ,j=nums.size()-; while(i<=j){ ; if(nums[mid]==target) return mid; ; ;…

Binary Search基础 应用于已排序的数据查找其中特定值,是折半查找最常的应用场景.相比线性查找(Linear Search),其时间复杂度减少到O(lgn).算法基本框架如下: //704. Binary Search int search(vector<int>& nums, int target) { //nums为已排序数组 ,j=nums.size()-; while(i<=j){ ; if(nums[mid]==target) return mid; ; ;…

题目来源 https://leetcode.com/problems/validate-binary-search-tree/ 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'…

Given n, how many structurally unique BST's (binary search trees) that store values 1...n? For example,Given n = 3, there are a total of 5 unique BST's. 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3   思路: 遇到二叉树,多半是分为左右子树两个问题递归下去. 由序列[1,…,m]和[i+1,…

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 subtree of a node contains only nodes with keys…

1.题目描述 2.问题分析 首先将二叉查找树使用中序遍历的方式将元素放入一个vector,然后在vector 中截取符合条件的数字. 3.代码 /** * Definition of TreeNode: * class TreeNode { * public: * int val; * TreeNode *left, *right; * TreeNode(int val) { * this->val = val; * this->left = this->right = NULL; *…

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 subtree of a node contains only nodes with keys…

题目: Given n, how many structurally unique BST's (binary search trees) that store values 1...n? For example, Given n = 3, there are a total of 5 unique BST's. 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3 解题: 用递归的思想,当仅仅有0个或是1个节点的时候.仅仅有一种.n个节点的时候有f…

原题链接在这里:https://leetcode.com/problems/verify-preorder-sequence-in-binary-search-tree/ 题目: Given an array of numbers, verify whether it is the correct preorder traversal sequence of a binary search tree. You may assume each number in the sequence is u…