432. 全 O(1) 的数据结构 实现一个数据结构支持以下操作: Inc(key) - 插入一个新的值为 1 的 key.或者使一个存在的 key 增加一,保证 key 不为空字符串. Dec(key) - 如果这个 key 的值是 1,那么把他从数据结构中移除掉.否者使一个存在的 key 值减一.如果这个 key 不存在,这个函数不做任何事情.key 保证不为空字符串. GetMaxKey() - 返回 key 中值最大的任意一个.如果没有元素存在,返回一个空字符串"". GetM…

题目: 使用栈实现队列的下列操作: push(x) -- 将一个元素放入队列的尾部. pop() -- 从队列首部移除元素. peek() -- 返回队列首部的元素. empty() -- 返回队列是否为空. 注意: 你只能使用标准的栈操作-- 也就是只有push to top, peek/pop from top, size, 和 is empty 操作是合法的. 你所使用的语言也许不支持栈.你可以使用 list 或者 deque (双端队列) 来模拟一个栈,只要是标准的栈操作即可. 假设所有…

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers. Ensure that numbers within the set are sorted in ascending order. Example 1…

Given a string S, you are allowed to convert it to a palindrome by adding characters in front of it. Find and return the shortest palindrome you can find by performing this transformation. For example: Given "aacecaaa", return "aaacecaaa&qu…

Given a 2D board and a list of words from the dictionary, find all words in the board. Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same le…

Design a data structure that supports the following two operations: void addWord(word)bool search(word) search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.…

There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1] Given the total number of courses and a l…

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by…

Say you have an array for which the ith element is the price of a given stock on day i. Design an algorithm to find the maximum profit. You may complete at most k transactions. 解题思路: https://leetcode.com/discuss/18330/is-it-best-solution-with-o-n-o-1…

Suppose a sorted array is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). Find the minimum element. The array may contain duplicates. 解题思路: 参考Java for LeetCode 081 Search in Rotated Sorted Array II J…