PAT1007 素数对猜想 (20 分)

题目描述

C++解法

#include<iostream>
using namespace std;
bool isprime(int a){
    for(int i=2;i*i<=a;i++)
        if(a%i==0) return false;
    return true;
}
int main(){
    int n,rst=0;
    cin>>n;
    for(int i=5;i<=n;i++)
        if(isprime(i-2)&&isprime(i)) rst++;
    cout<<rst;
    return 0;
}

python解法

N = int(input())

flag = [1]*(N+2)
flag[0] = flag[1] = 0
result = []

for i in range(2,N+1):
    if flag[i]:
        result.append(i)
        p = 2
        while i*p <= N:
            flag[i*p] = 0
            p += 1

c = 0
for i in range(len(result)-1):
    if (result[i+1] - result[i]) == 2:
        c += 1

print(c)