pengweixuan008的博客

题目：Count the number of prime numbers less than a non-negative number, n.代码：public class Solution {    public int countPrimes(int n) {        boolean [] a = new boolean[n];        int cou

Given an integer, write a function to determine if it is a power of two.方法：如果这个数是2的倍数（n%2==0），将这个数除以二（n /=2 ），循环上述操作，最后n==1返回true代码：public class Solution {    public boolean isPowerOfTwo

public Integer findGreatestSum(int[] arr){                    if(arr.length ==0)              return null;           int greatest = 0x80000000;          int curSum = 0;          for(int i 

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

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 代码：publ

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 its digits, and repeat the process until the number equ

Given an array of integers, find two numbers such that they add up to a specific target number.Input: numbers={2, 7, 11, 15}, target=9Output: index1=1, index2=2代码：public class Solution

public class Solution {    public int romanToInt(String s) {        char[] symbol = { 'I', 'V', 'X', 'L', 'C', 'D', 'M' };        int[] val = { 1, 5, 10, 50, 100, 500, 1000 };        Map map =