472A - Design Tutorial Learn from Math.cpp

/*
One way to create a task is to learn from math. You can generate some random math statement or modify some theorems to get something new and build a new task from that.

For example, there is a statement called the "Goldbach's conjecture". It says: "each even number no less than four can be expressed as the sum of two primes". Let's modify it. How about a statement like that: "each integer no less than 12 can be expressed as the sum of two composite numbers." Not like the Goldbach's conjecture, I can prove this theorem.

You are given an integer n no less than 12, express it as a sum of two composite numbers.

Input
The only line contains an integer n (12?=?n?=?106).

Output
Output two composite integers x and y (1?<?x,?y?<?n) such that x?+?y?=?n. If there are multiple solutions, you can output any of them.

Examples
inputCopy
12
outputCopy
4 8
inputCopy
15
outputCopy
6 9
inputCopy
23
outputCopy
8 15
inputCopy
1000000
outputCopy
500000 500000
Note
In the first example, 12 = 4 + 8 and both 4, 8 are composite numbers. You can output "6 6" or "8 4" as well.

In the second example, 15 = 6 + 9. Note that you can't output "1 14" because 1 is not a composite number.
*/



#include<bits/stdc++.h>
using namespace std;

bool isPrime(int n) {
	if (n <= 1) return false;
	if (n <=3) return true;
	if (n % 2== 0 || n % 3 == 0) return false;
	for (int i  = 5; i * i <= n; i += 6)
		if (n % i == 0 || n % (i + 2) == 0) return false;
	return true;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    
    int n;
    cin >> n;
    
    for (int x = 4; x < n; x++) {
    	if (!isPrime(x)) {
    		int y = n - x;
    		if (!isPrime(y)) {
    			cout << x << " " << y;
    			break;
			}
		}
	}
    

    return 0;
}