PAT B1007 素数对猜想 （20 分）

#include <stdio.h>
#include <algorithm>
#include <string>
#include <map>
#include <iostream>
#include <stack>
#include <math.h>
using namespace std;
const int maxn = 100010;
int index[maxn] = { 0 };
bool isPrime(int i){
    for (int k = 2; k <= sqrt(i); k++){
        if (i%k == 0)return false;
    }
    return true;
}
int main(){
    int n, count = 0;
    cin >> n;
    if (n == 1 || n == 2){
        cout << ‘0‘;
        return 0;
    }
    for (int i = 2; i <= n; i++){
        if (isPrime(i)){
            index[i] = 1;
            
        }
    }
    for (int i = 2; i <= n-2; i++){
        if(index[i]==1 && (index[i + 2] - index[i] == 0))count++;
    }
    cout << count;
    system("pause");
}