How to use the prime number judgment algorithm in C++
How to use the prime number judgment algorithm in C
Prime number judgment is a common problem in algorithms. It requires judging whether a given number is a prime number (prime number). In C, we can use different algorithms to solve this problem. This article will introduce two common prime number judgment algorithms and give corresponding code examples.
- Brute force method (brute force method)
Brute force method (violent method) is the most direct algorithm. Its idea is to compare a given number with all numbers less than the number. Perform the remainder operation. If there is a number that can divide the number, then the number is not a prime number, otherwise it is a prime number.
The following is an example of C code that uses brute force to determine whether a given number is prime:
#include <iostream> bool isPrime(int n) { if (n < 2) // 小于2的数都不是素数 return false; for (int i = 2; i * i <= n; i++) { if (n % i == 0) return false; } return true; } int main() { int num; std::cout << "请输入一个整数:"; std::cin >> num; if (isPrime(num)) std::cout << num << " 是素数。" << std::endl; else std::cout << num << " 不是素数。" << std::endl; return 0; }
- Sieve of Eratosthenes
Era The Tostoney sieve method is a prime number judgment algorithm based on the sieve method. Its idea is to first generate a table of all numbers starting from 2 to a given range, and then sift out the non-prime numbers one by one. What is left in the end is Prime number.
The following is a C code example that uses the sieve of Eratosthenes to determine whether a given number is a prime number:
#include <iostream> #include <vector> bool isPrime(int n) { if (n < 2) // 小于2的数都不是素数 return false; std::vector<bool> is_prime(n + 1, true); is_prime[0] = is_prime[1] = false; for (int i = 2; i * i <= n; i++) { if (is_prime[i]) { for (int j = i * i; j <= n; j += i) { is_prime[j] = false; } } } return is_prime[n]; } int main() { int num; std::cout << "请输入一个整数:"; std::cin >> num; if (isPrime(num)) std::cout << num << " 是素数。" << std::endl; else std::cout << num << " 不是素数。" << std::endl; return 0; }
The above is the C code of two common prime number determination algorithms Code example, by running this code, we can determine whether a given number is prime. Of course, both algorithms have their own advantages and disadvantages. In specific application scenarios, the appropriate algorithm needs to be selected based on the actual situation. I hope this article will be helpful to readers in understanding and using the prime number judgment algorithm in C.
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