284. 顶端迭代器 给定一个迭代器类的接口,接口包含两个方法: next() 和 hasNext().设计并实现一个支持 peek() 操作的顶端迭代器 – 其本质就是把原本应由 next() 方法返回的元素 peek() 出来. 示例: 假设迭代器被初始化为列表 [1,2,3]. 调用 next() 返回 1,得到列表中的第一个元素. 现在调用 peek() 返回 2,下一个元素.在此之后调用 next() 仍然返回 2. 最后一次调用 next() 返回 3,末尾元素.在此之后调用 has…

顶端迭代器 给定一个迭代器类的接口,接口包含两个方法: next() 和 hasNext().设计并实现一个支持 peek() 操作的顶端迭代器 -- 其本质就是把原本应由 next() 方法返回的元素 peek() 出来. 示例: 假设迭代器被初始化为列表 [1,2,3]. 调用 next() 返回 1,得到列表中的第一个元素. 现在调用 peek() 返回 2,下一个元素.在此之后调用 next() 仍然返回 2. 最后一次调用 next() 返回 3,末尾元素.在此之后调用 hasNext…

Given an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() operation -- it essentially peek() at the element that will be returned by the next call to next(). Example: Assume t…

Given an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() operation -- it essentially peek() at the element that will be returned by the next call to next(). Here is an exampl…

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…