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摘要：Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1 / \ 2 2 / 阅读全文

摘要：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 阅读全文

摘要：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 i 阅读全文

摘要：Subsets Given a set of distinct integers, S, return all possible subsets. Note: Elements in a subset must be in non-descending order. The solution set 阅读全文

摘要：Convert Sorted Array to Binary Search Tree Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 方法：将有序数组转 阅读全文

摘要：Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the dept 阅读全文

摘要：Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest l 阅读全文

摘要：Flatten Binary Tree to Linked List Given a binary tree, flatten it to a linked list in-place. For example,Given 1 / \ 2 5 / \ \ 3 4 6 The flattened tr 阅读全文

摘要：Path Sum Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the giv 阅读全文

摘要：Best Time to Buy and Sell Stock Say you have an array for which the ith element is the price of a given stock on day i. If you were only permitted to 阅读全文

摘要：Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longes 阅读全文

摘要：Palindrome Partitioning Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome parti 阅读全文

摘要：Given a string S and a string T, count the number of distinct subsequences of T in S. A subsequence of a string is a new string which is formed from t 阅读全文

摘要：Given a binary tree, find the maximum path sum. The path may start and end at any node in the tree. For example:Given the below binary tree, 1 / \ 2 3 阅读全文

摘要：Given an unsorted array of integers, find the length of the longest consecutive elements sequence. For example,Given [100, 4, 200, 1, 3, 2],The longes 阅读全文

摘要：Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 whic 阅读全文

摘要：Reverse digits of an integer. Example1: x = 123, return 321Example2: x = -123, return -321 click to show spoilers. Have you thought about this? Here a 阅读全文

摘要：Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example,"A man, a plan, a canal: Pan 阅读全文

摘要：Determine whether an integer is a palindrome. Do this without extra space. click to show spoilers. Some hints: Could negative integers be palindromes? 阅读全文

摘要：There are N gas stations along a circular route, where the amount of gas at station i is gas[i]. You have a car with an unlimited gas tank and it cost 阅读全文

摘要：Given an input string, reverse the string word by word. For example,Given s = "the sky is blue",return "blue is sky the". click to show clarification. 阅读全文

摘要：Maximum Subarray Find the contiguous subarray within an array (containing at least one number) which has the largest sum. For example, given the array 阅读全文

摘要：一. 全排列递归算法 1. 数据没有重复的情况下 算法：每个元素依次与后面的数进行交换 例子：假设元素为123，则递归交换事例如下： 2. 数据有重复的情况下、 算法：在没有数据重复的全排列下，交换需要加上前提条件，即元素应该和后面没有重复出现的数字进行交换，即当访问到第k个元素的时候，如果 [k, 阅读全文

摘要：1、问题定义可以简化如下：在不知道文件总行数的情况下，如何从文件中随机的抽取一行，并且每行被抽中的概率相等？ 首先想到的是我们做过类似的题目吗？当然，在知道文件行数的情况下，我们可以很容易的用C运行库的rand()函数随机的获得一个行数，从而随机的取出一行，但是，当前的情况是不知道行数，这样如何求呢... 阅读全文

摘要：在严老师的数据结构书上学习了各种排序算法，比如插入排序，选择排序，堆排序，快速排序，归并排序等，不过书上代码的应用场景均是底层结构是顺序存储的情况，即数组。 今天总结下对于单链表，常用的排序算法能否使用。由于希尔排序、堆排序、计数排序都要求随机访问，而单链表只能顺序访问，故这 3 种是不能用于单向链 阅读全文

摘要：首先讨论下有环单链表相关问题 1. 判断单链表是否有环 使用slow，fast指针从头开始扫描链表，slow指针每次走一步，fast指针每次走两步，如果链表有环，那么fast指针一定会追上slow指针，否则，fast指针会遇到null。 2. 求有环单链表的环长 设环长为R，当fast，slow指针 阅读全文

摘要：Construct Binary Tree from Preorder and Inorder Traversal Given preorder and inorder traversal of a tree, construct the binary tree. Note: You may ass 阅读全文

摘要：Binary Tree Level Order Traversal Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level) 阅读全文

摘要：Binary Tree Preorder Traversal Given a binary tree, return the preorder traversal of its nodes' values. For example: Given binary tree {1,#,2,3}, 1 \ 阅读全文

摘要：Single Number Given an array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear 阅读全文