C++ で数値を可能な最大数の素数の合計として表現します。

Input: N = 7
Output: 2 2 3
Explanation: 7 can be represented as the sum of two 2’s and a 3 which are the maximum possible prime numbers.

Input : N = 17
Output: 2 2 2 2 2 2 2 3

#include <bits/stdc++.h>
using namespace std;
int main(){
   int N = 7;
   // checking if N is odd,
   // If yes, then print 3
   // and subtract 3 from N.
   if (N & 1 == 1) {
      cout << "3 +";
      N -= 3;
   }
   // // keep subtracting and printing 2
   // until N is becomes 0.
   while (N!=2) {
      cout << " 2 +";
      N -= 2;
   }
   cout << " 2";
   return 0;
}

3 + 2 + 2