JackZhangNJU的专栏

Implement the following operations of a stack using queues.push(x) – Push element x onto stack. pop() – Removes the element on top of the stack. top() – Get the top element. empty() – Return whet...

题意如上图，这个题主要就是如何判断一个数字是不是神奇数字，这个技术拆分出所有的位，然后DFS深度优先遍历判断。import java.util.ArrayList;import java.util.List;public class Solution{ /* * 神奇数字的判断 * */ boolean getCount(int num) {

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.OJ’s undirected graph serialization: Nodes are labeled uniquely.We use # as a separator for each nod...

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.Return a deep copy of the list.本题题意就是复制链表，注意使用HashMap等结构保存相关信息，这样...

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.get(key) - Get the value (will always be positive) of the key if the k

Implement the following operations of a queue using stacks.push(x) – Push element x to the back of queue. pop() – Removes the element from in front of queue. peek() – Get the front element. empty...

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) – Push element x onto stack. pop() – Removes the element on top of the stack. top() – Get 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 retur...

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.Calling next() will return the next smallest number in the BST.Note: next() and...

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2.Note:The length of both num1 and num2 is < 110. Both num1 and num2 contains only digit...

Implement wildcard pattern matching with support for ‘?’ and ‘*’.‘?’ Matches any single character. ‘*’ Matches any sequence of characters (including the empty sequence).The matching should cover ...

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.Example: Given nums = [-2, 0, 3, -5, 2, -1]sumRange(0, 2) -> 1 sumRange(2, 5) -> -1 su...

Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2). Range Sum Query 2D The above rectang...

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 letter...

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 horiz...

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 given sum.For example: Given the below binary tree and sum = 2

Given a binary tree, flatten it to a linked list in-place.For example, Given 1 / \ 2 5 / \ \ 3 4 6The flattened tree should look like: 1 \ 2 \ 3

Given a binary treestruct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next;}Populate each next pointer to point to its next right node. If there is no next right node,

Given numRows, generate the first numRows of Pascal’s triangle.For example, given numRows = 5, Return[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]这个就是中国最伟大的杨辉三角形的问题。代码如下：import

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Note: The solution set must not contain duplic

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.Seen this question in a real interview before? Yes简单的归并排序，

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:[ “((()))”, “(()())”, “(())()”, “()(())”,

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.提议很简单，就是归并排序。首先想到的即使逐个归并得到最终的结果，但是会超时，这是因为这种会造成数组的size大小不一样，导致归并排序的时间变长；最好的做法是两两合并，然后在两两合并，这样不会超时， 需要注

Given an index k, return the kth row of the Pascal’s triangle.For example, given k = 3, Return [1,3,3,1].就是中国最伟大的杨辉三角形。代码如下：import java.util.ArrayList;import java.util.List;public class So

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.For example, given the following triangle [ [2], [3,4], [6

Given a linked list, swap every two adjacent nodes and return its head.For example, Given 1->2->3->4, you should return the list as 2->1->4->3.Your algorithm should use only constant space. You may no

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.k is a positive integer and is less than or equal to the length of the linked list. If the number of nod

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.For example, Given [3,2,1,5,6,4] and k = 2, return 5.这...

Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the array, and it should return false if every element is

Given an array of integers, every element appears twice except for one. Find that single one.Note: Your algorithm should have a linear runtime complexity. Could you implement it without using extra me

Given an array of integers, every element appears three times except for one, which appears exactly once. Find that single one.Note: Your algorithm should have a linear runtime complexity. Could you i

Given a singly linked list L: L0?L1?…?Ln-1?Ln, reorder it to: L0?Ln?L1?Ln-1?L2?Ln-2?…You must do this in-place without altering the nodes’ values.For example, Given {1,2,3,4}, reorder it to {1,4,2,3}

Sort a linked list using insertion sort.本题就是要做链表的插入排序。代码如下：/*class ListNode { int val; ListNode next; ListNode(int x) { val = x; }}*//* * 链表的插入排序 * */public class Solution {

Sort a linked list in O(n log n) time using constant space complexity.本题就是考察的是链表的归并排序。代码如下：/*class ListNode { int val; ListNode next; ListNode(int x) { val = x; }}*/public class So

Evaluate the value of an arithmetic expression in Reverse Polish Notation.Valid operators are +, -, *, /. Each operand may be an integer or another expression.Some examples: [“2”, “1”, “+”, “3”, ““]

Implement strStr().Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.strstr(str1,str2) 函数用于判断字符串str2是否是str1的子串，我这里是直接循环判断的。代码如下：public class Solut

Divide two integers without using multiplication, division and mod operator.If it is overflow, return MAX_INT.这种题我不喜欢，这个是网上查阅的答案，这道题就这样吧。代码如下：public class Solution { public int divide(int dividend,

You are given a string, s, and a list of words, words, that are all of the same length. Find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once and wit

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.If such arrangement is not possible, it must rearrange it as the lowest possible orde