Description: Count the number of prime numbers less than a non-negative number, n. 题解:就是线性筛素数的模板题. class Solution { public: int countPrimes(int n) { ; vector<,); ;i<n;i++){ if(is_prime[i]){ ans++; *i;j<n;j+=i){ is_prime[j]=; } } } return ans; } }…

题目大意 https://leetcode.com/problems/count-primes/description/ 204. Count Primes Count the number of prime numbers less than a non-negative number, n. Example: Input: 10Output: 4Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.…

Count the number of prime numbers less than a non-negative number, n. Example: Input: 10 Output: 4 Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7. References: How Many Primes Are There? Sieve of Eratosthenes Credits:Special…

Description: Count the number of prime numbers less than a non-negative number, n click to show more hints. References: How Many Primes Are There? Sieve of Eratosthenes Credits:Special thanks to @mithmatt for adding this problem and creating all test…

Description: Count the number of prime numbers less than a non-negative number, n. 解题思路: 空间换时间,开一个空间为n的数组,因为非素数至少可以分解为一个素数,因此遇到素数的时候,将其有限倍置为非素数,这样动态遍历+构造下来,没有被设置的就是素数. public int countPrimes(int n) { if (n <= 2) return 0; boolean[] notPrime = new boo…

题意:统计小于n的质数个数. 作为一个无节操的楼主,表示用了素数筛法,并没有用线性素数筛法. 是的,素数筛法并不是该题最佳的解法,线性素数筛法才是. 至于什么是素数筛法,请百度吧. class Solution { public: int countPrimes(int n) { bool *isp= new bool[n]; ; i < n; ++i) { isp[i]= true; } ; i * i< n; ++i)//素数筛法 { if(isp[i]){ for(int j = i +…

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. 解析:大于1的自然数,该自然数能被1和它本身整除,那么该自然数称为素数. 方法一:暴力破解,时间复杂度为O(N^2) 代码如下: public class…

题目描述: Description: Count the number of prime numbers less than a non-negative number, n. 解题思路: Let's start with a isPrime function. To determine if a number is prime, we need to check if it is not divisible by any number less than n. The runtime comp…

Count the number of prime numbers less than a non-negative number, n. 问题:找出所有小于 n 的素数. 题目很简洁,但是算法实现的优化层次有很多层.其中最主要思想的是采用 Sieve of Eratosthenes 算法来解答. 大思路为: 找出 n 范围内所有合数,并做标记. 未做标记的即为素数,统计未做标记的数个数即为原题目解. 如何找到 n 范围内所有合数? 将第一个素数 2 赋值给 i. 当 i 小于 n 时:(2)…

原题 原题链接 Description: Count the number of prime numbers less than a non-negative number, n. 计算小于非负数n的素数个数. 思路 这题用埃拉托斯特尼筛法来做效果比较好,普通的方法基本会TLE.但是在用了埃拉托斯特尼筛法之后,还有一些细节值得注意: (1)首先我们该用 i*i<=n 替代 i<=sqrt(n) 来避免使用 sqrt() ,因为sqrt()的操作是比较expensive的. (2)当要表示两个状…