ljffdream的专栏

【题目】A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).The robot can only move either down or right at any point in time. The robot is trying to

【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.Hint:Let's

[题目]Given an integer, write a function to determine if it is a power of two.[思路]这道题的思路还是蛮简单的说,0的时候是false,不可能是2 的倍数。8/2 =4 4/2 =2 2/2 =1。最后肯定是得1。7%2 ！=0不能被2整除肯定是不行的。[代码]public class S

【题目】Implement atoi to convert a string to an integer.Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possibl

【题目】Reverse digits of an integer.Example1: x = 123, return 321Example2: x = -123, return -321Have you thought about this?Here are some good questions to ask before coding. Bonus po

【题目】Given an integer n, return the number of trailing zeroes in n!.Note: Your solution should be in logarithmic time complexity.Credits:Special thanks to @ts for adding this problem an

【题目】Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.The Sudoku board could be partially filled, where empty cells are filled with the character '.'.A parti

[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 s

【题目】 Find the total area covered by two rectilinear rectangles in a 2D plane.Each rectangle is defined by its bottom left corner and top right corner as shown in the figure. Rectangle Area图片： https:

[题目]Implement a basic calculator to evaluate a simple expression string.The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers an

【题目】Related to question Excel Sheet Column TitleGiven a column title as appear in an Excel sheet, return its corresponding column number.For example: A -> 1 B -> 2 C -> 3

【题目】Given a positive integer, return its corresponding column title as appear in an Excel sheet.For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27 -> AA 28 -> AB

【题目】Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.【分析】只要是遵守那个转换规则就好吧。然后就是数学处理。【代码1】private static LinkedHashMap numToRoman

【题目】【思路】My idea is simple: store states of each row in the first of that row, and store states of each column in the first of that column. Because the state of row0 and the state of column0