Prime Sum
Problem Description
Find all pairs of prime numbers (A, B) such that A<=B and their sum is also a prime number and does not exceed N.
Input
The input of the problem consists of the only integer N (1<=N<=10^6).
Output
On the first line of the output file write the number of pairs meeting the requirements. Then output all pairs one per line (two primes separated by a space).
Sample test(s)
Input
4
Output
0
Solution
代码语言：javascript复制#include <bits/stdc .h>
int main() {
std::ios::sync_with_stdio(false);
int n{};
std::cin >> n;
std::vector<bool> visit(n 1, false);
std::vector<int> prime{};
for(unsigned long i = 2; i < visit.size(); i ) {
if(visit[i]) {
continue;
}
prime.push_back(i);
for(unsigned long j = i * 2; j < visit.size(); j = i) {
visit[j] = true;
}
}
int count = 0;
for(unsigned long i = 1; i < prime.size(); i ) {
if(prime[i] - prime[i - 1] == 2) {
count = 1;
}
}
std::cout << count << std::endl;
for(unsigned long i = 1; i < prime.size(); i ) {
if(prime[i] - prime[i - 1] == 2) {
std::cout << 2 << " " << prime[i - 1] << std::endl;
}
}
return 0;
}
