洛谷 P1304 哥德巴赫猜想 题解C/C++

//P1304 哥德巴赫猜想
//#define LOCAL
#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <algorithm>
#include <cctype>
#include <sstream>
#define inf 0x3f3f3f3f
#define eps 1e-6
using namespace std;
#define clr(x) memset(x,0,sizeof((x)))
const int maxn = 1e5+1;//2e6+1
#define MAX(a,b,c) ((a)>(b)?((a)>(c)?(a):(c)):((b)>(c)?(b):(c)))
#define _max(a,b) ((a) > (b) ? (a) : (b))
#define _min(a,b) ((a) < (b) ? (a) : (b))
#define _for(a,b,c) for(int a = b;a<c;a++)
int is_prime(int x) {
    
    //判断质数
	if(x<=1)return 0;
	if(x==2||x==3)return 1;
	if(x%6!=1 && x%6!=5)return 0;
	for(int i =5;i*i<=x;i+=6) {
    
    
		if(x%i==0||x%(i+2)==0)return 0;
	}
	return 1;
}
int main()
{
    
    
#ifdef LOCAL 
	freopen("data.in","r",stdin);
	freopen("data.out","w",stdout);
#endif
	int n;
	cin>>n;
	for(int i = 4;i<=n;i+=2) {
    
    
		for(int j = 2;j<i;j++) {
    
    
			if(is_prime(j)&&is_prime(i-j)) {
    
    
				printf("%d=%d+%d\n",i,j,i-j);
				break;
			}
		}
	}
    return 0;
}