python/TangDou/XiTi/1145.cpp

#include <bits/stdc++.h>

using namespace std;

//判断是不是质数
bool isPrime(int n) { //最快的方法
    if (n < 2) return false;
    if (n == 2 || n == 3) return true;
    if (n % 6 != 1 && n % 6 != 5) return false;
    for (int i = 5; i <= floor(sqrt(n)); i += 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
    return true;
}

int main() {
    int n;
    cin >> n;

    //1、找到所有比当前数小的质数
    int a[100] = {0};
    int k = 0;
    for (int i = 2; i <= n; ++i) {
        if (isPrime(i)) {
            a[k++] = i;
        }
    }
    //2、两两配对，是不是加在一起等于当前数
    bool found = false;
    for (int i = 0; i < k; ++i) {
        for (int j = 1; j <= k; ++j) {
            if (a[i] + a[j] == n) {
                cout << n << "=" << a[i] << "+" << a[j] << endl;
                found = true;
                break;
            }
        }
        if (found) break;
    }
    return 0;
}