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法律研究使用輪式篩法生成給定範圍內的素數的 C++ 程式
輪篩法用於尋找給定範圍內的素數。輪式分解是一種手動執行埃拉託斯特尼篩法以將素數與合數分開的圖形方法，即篩選法。
在此方法中，內圓內的素數在其與其他圓內的位置上具有其倍數，形成素數和其倍數的輻條。內圓中這些素數的倍數形成外圓中合數的輻條。
演算法
Begin Define max number gen_sieve_primes() Declare c Assign c = 2 For p = 2 to max number If prime[p]==0 prime[p]=1 Mul = p multiply c For Mul less than max number prime[Mul] = -1 Increment c Mul = p multiply c Done Done Print_all_prime() Assign c=0 For i = 0 to max number if (prime[i] == 1) Increment c If c less than 4 Switch(c) Case 1 Print 1st prime number Case 2 Print 2nd prime number Case 3 Print 3rd prime number Else Print nth prime number End
示例程式碼
#include <iostream>
using namespace std;
#define MAX_NUMBER 40
int prime[MAX_NUMBER];
void gen_sieve_prime(void) {
for (int p = 2; p < MAX_NUMBER; p++) {
if (prime[p] == 0)
prime[p] = 1;
int c = 2;
int mul = p * c;
for (; mul < MAX_NUMBER;) {
prime[mul] = -1;
c++;
mul = p * c;
}
}
}
void print_all_prime() {
int c = 0;
for (int i = 0; i < MAX_NUMBER; i++) {
if (prime[i] == 1) {
c++;
if (c < 4) {
switch (c) {
case 1:
cout << c << "st prime is: " << i << endl;
break;
case 2:
cout << c << "nd prime is: " << i << endl;
break;
case 3:
cout << c << "rd prime is: " << i << endl;
break;
default:
break;
}
}else
cout << c << "th prime is: " << i << endl;
}
}
}
int main() {
gen_sieve_prime();
print_all_prime();
return 0;
}輸出
1st prime is: 2 2nd prime is: 3 3rd prime is: 5 4th prime is: 7 5th prime is: 11 6th prime is: 13 7th prime is: 17 8th prime is: 19 9th prime is: 23 10th prime is: 29 11th prime is: 31 12th prime is: 37
更新於：30-Jul-2019
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