toyijiu的专栏

题目There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third round, you toggle every third bulb (turning on if it’s off or turning off

题目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”, “

题目Suppose an array sorted in ascending order 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.You may assume no duplicate exi

题目Given an integer, write a function to determine if it is a power of three.Follow up: Could you do it without using any loop / recursion?Credits: Special thanks to @dietpepsi for adding this problem

题目Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.You should try to do it in pl

题目Given an integer matrix, find the length of the longest increasing path.From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of

题目Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1’s in their binary representation and return them as an array.Example: For num = 5 you

题目Given an integer (signed 32 bits), write a function to check whether it is a power of 4.Example: Given num = 16, return true. Given num = 5, return false.Follow up: Could you solve it without loops/

题目Write a program to find the node at which the intersection of two singly linked lists begins.For example, the following two linked lists:A: a1 → a2 ↘

题目Given a positive integer, return its corresponding column title as appear in an Excel sheet.For example:1 -> A2 -> B3 -> C...26 -> Z27 -> AA28 -> AB Credits: Special thanks to @ifanchu for ad

题目Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.You may assume that the array is non-empty and the majority element alway

题目You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent hous

题目Write an algorithm to determine if a number is “happy”.A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of

题目Remove all elements from a linked list of integers that have value val.Example Given: 1 –> 2 –> 6 –> 3 –> 4 –> 5 –> 6, val = 6 Return: 1 –> 2 –> 3 –> 4 –> 5Credits: Special thanks to @mithmatt for

题目Description:Count the number of prime numbers less than a non-negative number, n.Credits: Special thanks to @mithmatt for adding this problem and creating all test cases.思路普通的计算素数个数效率太低，这里用空间换时间，搞一个

题目Reverse a singly linked list.click to show more hints.Subscribe to see which companies asked this question.Show Tags Show Similar Problems思路两个指针一前一后遍历翻转链表指向，注意最后要把最开始的head的next指针弄成NULL代码/** * Defin

题目Given a positive integer n, break it into the sum of at least two positive integers and maximize the product of those integers. Return the maximum product you can get.For example, given n = 2, return

题目Write a function that takes a string as input and returns the string reversed.Example: Given s = “hello”, return “olleh”.Subscribe to see which companies asked this question.思路比较简单，两个index往中间靠，并互换字符

题目Write a function that takes a string as input and reverse only the vowels of a string.Example 1: Given s = “hello”, return “holle”.Example 2: Given s = “leetcode”, return “leotcede”.Note: The vowe

题目The Hamming distance between two integers is the number of positions at which the corresponding bits are different.Given two integers x and y, calculate the Hamming distance.Note: 0 ≤ x, y < 231.Exa

题目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 wheth

题目Given an 2D board, count how many battleships are in it. The battleships are represented with ‘X’s, empty slots are represented with ‘.’s. You may assume the following rules:You receive a valid board

题目Write a program that outputs the string representation of numbers from 1 to n.But for multiples of three it should output “Fizz” instead of the number and for the multiples of five output “Buzz”. For

题目Invert a binary tree. 4/ \ 2 7 / \ / \ 1 3 6 9 to 4 / \ 7 2 / \ / \ 9 6 3 1 Trivia: This problem was inspired by this original tweet by Max Howell:

题目Given a sorted integer array without duplicates, return the summary of its ranges.For example, given [0,1,2,4,5,7], return [“0->2”,”4->5”,”7”].Credits: Special thanks to @jianchao.li.fighter for add

题目Given an integer, write a function to determine if it is a power of two.Credits: Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.Subscribe to see which com

题目Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.Find all the elements of [1, n] inclusive that do not appear in this array.Could y

题目Given two strings s and t which consist of only lowercase letters.String t is generated by random shuffling string s and then add one more letter at a random position.Find the letter that was added i

题目Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.For example:Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit,

题目Given an array of numbers nums, in which exactly two elements appear only once and all the other elements appear exactly twice. Find the two elements that appear only once.For example:Given nums = [1

题目Given an array nums, write a function to move all 0’s to the end of it while maintaining the relative order of the non-zero elements.For example, given nums = [0, 1, 0, 3, 12], after calling your fun

题目You are playing the following Nim Game with your friend: There is a heap of stones on the table, each time one of you take turns to remove 1 to 3 stones. The one who removes the last stone will be th

题目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 sumRange(0,

题目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 as many transactions as you like (ie, buy one a

题目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 as many transactions as you like (ie, buy one a

题目Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it

题目Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.Example: Given a = 1 and b = 2, return 3.Credits: Special thanks to @fujiaozhu for adding this problem

题目Given an integer, return its base 7 string representation.Example 1: Input: 100 Output: “202” Example 2: Input: -7 Output: “-10” Note: The input will be in range of [-1e7, 1e7].Subscribe to see

题目Given a linked list, return the node where the cycle begins. If there is no cycle, return null.Note: Do not modify the linked list.Follow up: Can you solve it without using extra space?Subscribe to

Write a function that takes a string as input and returns >the string reversed. Example: Given s = “hello”, return “olleh”. char* reverseString(char* s) { char tempChar; int prePoi